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![Paul E. McKenney](/assets/img/avatar_default.png)
Because RCU's quiescent-state-forcing mechanism is used to drive the full-system-idle state machine, and because this mechanism is executed by RCU's grace-period kthreads, this commit forces these kthreads to run on the timekeeping CPU (tick_do_timer_cpu). To do otherwise would mean that the RCU grace-period kthreads would force the system into non-idle state every time they drove the state machine, which would be just a bit on the futile side. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Lai Jiangshan <laijs@cn.fujitsu.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2797 lines
81 KiB
C
2797 lines
81 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/smpboot.h>
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#include "time/tick-internal.h"
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#define RCU_KTHREAD_PRIO 1
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#ifdef CONFIG_RCU_BOOST
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#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
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#else
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#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
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#endif
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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static char __initdata nocb_buf[NR_CPUS * 5];
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary. If you like #ifdef, you
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* will love this function.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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#ifdef CONFIG_RCU_TRACE
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pr_info("\tRCU debugfs-based tracing is enabled.\n");
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#endif
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#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
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pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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CONFIG_RCU_FANOUT);
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#endif
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#ifdef CONFIG_RCU_FANOUT_EXACT
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pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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#endif
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#ifdef CONFIG_RCU_FAST_NO_HZ
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pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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#endif
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#ifdef CONFIG_PROVE_RCU
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pr_info("\tRCU lockdep checking is enabled.\n");
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#endif
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#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
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pr_info("\tRCU torture testing starts during boot.\n");
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#endif
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#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
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pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
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#endif
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#if defined(CONFIG_RCU_CPU_STALL_INFO)
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pr_info("\tAdditional per-CPU info printed with stalls.\n");
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#endif
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#if NUM_RCU_LVL_4 != 0
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pr_info("\tFour-level hierarchy is enabled.\n");
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#endif
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if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_NOCB_CPU
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#ifndef CONFIG_RCU_NOCB_CPU_NONE
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if (!have_rcu_nocb_mask) {
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zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
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have_rcu_nocb_mask = true;
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}
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#ifdef CONFIG_RCU_NOCB_CPU_ZERO
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pr_info("\tOffload RCU callbacks from CPU 0\n");
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cpumask_set_cpu(0, rcu_nocb_mask);
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
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#ifdef CONFIG_RCU_NOCB_CPU_ALL
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pr_info("\tOffload RCU callbacks from all CPUs\n");
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cpumask_setall(rcu_nocb_mask);
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
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#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
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if (have_rcu_nocb_mask) {
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cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
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pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
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if (rcu_nocb_poll)
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pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
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}
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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}
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#ifdef CONFIG_TREE_PREEMPT_RCU
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RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
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static struct rcu_state *rcu_state = &rcu_preempt_state;
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static int rcu_preempted_readers_exp(struct rcu_node *rnp);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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pr_info("Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/*
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* Return the number of RCU-preempt batches processed thus far
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* for debug and statistics.
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*/
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long rcu_batches_completed_preempt(void)
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{
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return rcu_preempt_state.completed;
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
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/*
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* Return the number of RCU batches processed thus far for debug & stats.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_batches_completed_preempt();
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}
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EXPORT_SYMBOL_GPL(rcu_batches_completed);
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/*
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* Force a quiescent state for preemptible RCU.
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*/
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void rcu_force_quiescent_state(void)
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{
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force_quiescent_state(&rcu_preempt_state);
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}
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EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* not in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* Unlike the other rcu_*_qs() functions, callers to this function
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* must disable irqs in order to protect the assignment to
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* ->rcu_read_unlock_special.
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*/
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static void rcu_preempt_qs(int cpu)
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{
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struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
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if (rdp->passed_quiesce == 0)
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trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
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rdp->passed_quiesce = 1;
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current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable preemption.
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*/
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static void rcu_preempt_note_context_switch(int cpu)
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{
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struct task_struct *t = current;
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unsigned long flags;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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if (t->rcu_read_lock_nesting > 0 &&
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(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
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/* Possibly blocking in an RCU read-side critical section. */
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rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
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rnp = rdp->mynode;
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raw_spin_lock_irqsave(&rnp->lock, flags);
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t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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t->rcu_blocked_node = rnp;
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/*
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* If this CPU has already checked in, then this task
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* will hold up the next grace period rather than the
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* current grace period. Queue the task accordingly.
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* If the task is queued for the current grace period
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* (i.e., this CPU has not yet passed through a quiescent
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* state for the current grace period), then as long
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* as that task remains queued, the current grace period
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* cannot end. Note that there is some uncertainty as
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* to exactly when the current grace period started.
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* We take a conservative approach, which can result
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* in unnecessarily waiting on tasks that started very
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* slightly after the current grace period began. C'est
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* la vie!!!
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*
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* But first, note that the current CPU must still be
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* on line!
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*/
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WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
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list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
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rnp->gp_tasks = &t->rcu_node_entry;
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#ifdef CONFIG_RCU_BOOST
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if (rnp->boost_tasks != NULL)
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rnp->boost_tasks = rnp->gp_tasks;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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} else {
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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if (rnp->qsmask & rdp->grpmask)
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rnp->gp_tasks = &t->rcu_node_entry;
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}
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trace_rcu_preempt_task(rdp->rsp->name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gpnum
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: rnp->gpnum + 1);
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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} else if (t->rcu_read_lock_nesting < 0 &&
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t->rcu_read_unlock_special) {
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/*
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* Complete exit from RCU read-side critical section on
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* behalf of preempted instance of __rcu_read_unlock().
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*/
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rcu_read_unlock_special(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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local_irq_save(flags);
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rcu_preempt_qs(cpu);
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local_irq_restore(flags);
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}
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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return rnp->gp_tasks != NULL;
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}
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/*
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* Record a quiescent state for all tasks that were previously queued
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* on the specified rcu_node structure and that were blocking the current
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* RCU grace period. The caller must hold the specified rnp->lock with
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* irqs disabled, and this lock is released upon return, but irqs remain
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* disabled.
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*/
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static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
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__releases(rnp->lock)
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{
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unsigned long mask;
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struct rcu_node *rnp_p;
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if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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return; /* Still need more quiescent states! */
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}
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rnp_p = rnp->parent;
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if (rnp_p == NULL) {
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/*
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* Either there is only one rcu_node in the tree,
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* or tasks were kicked up to root rcu_node due to
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* CPUs going offline.
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*/
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rcu_report_qs_rsp(&rcu_preempt_state, flags);
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return;
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}
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/* Report up the rest of the hierarchy. */
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mask = rnp->grpmask;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
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rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
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}
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/*
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* Advance a ->blkd_tasks-list pointer to the next entry, instead
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* returning NULL if at the end of the list.
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*/
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static struct list_head *rcu_next_node_entry(struct task_struct *t,
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struct rcu_node *rnp)
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{
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struct list_head *np;
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np = t->rcu_node_entry.next;
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if (np == &rnp->blkd_tasks)
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np = NULL;
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return np;
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}
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/*
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* Handle special cases during rcu_read_unlock(), such as needing to
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* notify RCU core processing or task having blocked during the RCU
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* read-side critical section.
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*/
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void rcu_read_unlock_special(struct task_struct *t)
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{
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int empty;
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int empty_exp;
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int empty_exp_now;
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unsigned long flags;
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struct list_head *np;
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#ifdef CONFIG_RCU_BOOST
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struct rt_mutex *rbmp = NULL;
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#endif /* #ifdef CONFIG_RCU_BOOST */
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struct rcu_node *rnp;
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int special;
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/* NMI handlers cannot block and cannot safely manipulate state. */
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if (in_nmi())
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return;
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local_irq_save(flags);
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/*
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* If RCU core is waiting for this CPU to exit critical section,
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* let it know that we have done so.
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*/
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special = t->rcu_read_unlock_special;
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if (special & RCU_READ_UNLOCK_NEED_QS) {
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rcu_preempt_qs(smp_processor_id());
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}
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/* Hardware IRQ handlers cannot block. */
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if (in_irq() || in_serving_softirq()) {
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local_irq_restore(flags);
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return;
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}
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/* Clean up if blocked during RCU read-side critical section. */
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if (special & RCU_READ_UNLOCK_BLOCKED) {
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t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
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/*
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* Remove this task from the list it blocked on. The
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* task can migrate while we acquire the lock, but at
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* most one time. So at most two passes through loop.
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*/
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for (;;) {
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rnp = t->rcu_blocked_node;
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raw_spin_lock(&rnp->lock); /* irqs already disabled. */
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if (rnp == t->rcu_blocked_node)
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break;
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raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
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}
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empty = !rcu_preempt_blocked_readers_cgp(rnp);
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empty_exp = !rcu_preempted_readers_exp(rnp);
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smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
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np = rcu_next_node_entry(t, rnp);
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list_del_init(&t->rcu_node_entry);
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t->rcu_blocked_node = NULL;
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trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
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rnp->gpnum, t->pid);
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if (&t->rcu_node_entry == rnp->gp_tasks)
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rnp->gp_tasks = np;
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if (&t->rcu_node_entry == rnp->exp_tasks)
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rnp->exp_tasks = np;
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#ifdef CONFIG_RCU_BOOST
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if (&t->rcu_node_entry == rnp->boost_tasks)
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rnp->boost_tasks = np;
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/* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
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if (t->rcu_boost_mutex) {
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rbmp = t->rcu_boost_mutex;
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t->rcu_boost_mutex = NULL;
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}
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the current list, and if
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* we aren't waiting on any CPUs, report the quiescent state.
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* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
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* so we must take a snapshot of the expedited state.
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*/
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empty_exp_now = !rcu_preempted_readers_exp(rnp);
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if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
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trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
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rnp->gpnum,
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0, rnp->qsmask,
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rnp->level,
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rnp->grplo,
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rnp->grphi,
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!!rnp->gp_tasks);
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rcu_report_unblock_qs_rnp(rnp, flags);
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} else {
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raw_spin_unlock_irqrestore(&rnp->lock, flags);
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}
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#ifdef CONFIG_RCU_BOOST
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/* Unboost if we were boosted. */
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if (rbmp)
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rt_mutex_unlock(rbmp);
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#endif /* #ifdef CONFIG_RCU_BOOST */
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/*
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* If this was the last task on the expedited lists,
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* then we need to report up the rcu_node hierarchy.
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*/
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if (!empty_exp && empty_exp_now)
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rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
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} else {
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local_irq_restore(flags);
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}
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period on the specified rcu_node structure.
|
|
*/
|
|
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return;
|
|
}
|
|
t = list_entry(rnp->gp_tasks,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
|
|
sched_show_task(t);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_INFO
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
|
|
rnp->level, rnp->grplo, rnp->grphi);
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return 0;
|
|
rcu_print_task_stall_begin(rnp);
|
|
t = list_entry(rnp->gp_tasks,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
pr_cont(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
rcu_print_task_stall_end();
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
|
|
* must be held by the caller.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
|
|
if (!list_empty(&rnp->blkd_tasks))
|
|
rnp->gp_tasks = rnp->blkd_tasks.next;
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Handle tasklist migration for case in which all CPUs covered by the
|
|
* specified rcu_node have gone offline. Move them up to the root
|
|
* rcu_node. The reason for not just moving them to the immediate
|
|
* parent is to remove the need for rcu_read_unlock_special() to
|
|
* make more than two attempts to acquire the target rcu_node's lock.
|
|
* Returns true if there were tasks blocking the current RCU grace
|
|
* period.
|
|
*
|
|
* Returns 1 if there was previously a task blocking the current grace
|
|
* period on the specified rcu_node structure.
|
|
*
|
|
* The caller must hold rnp->lock with irqs disabled.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
struct list_head *lp;
|
|
struct list_head *lp_root;
|
|
int retval = 0;
|
|
struct rcu_node *rnp_root = rcu_get_root(rsp);
|
|
struct task_struct *t;
|
|
|
|
if (rnp == rnp_root) {
|
|
WARN_ONCE(1, "Last CPU thought to be offlined?");
|
|
return 0; /* Shouldn't happen: at least one CPU online. */
|
|
}
|
|
|
|
/* If we are on an internal node, complain bitterly. */
|
|
WARN_ON_ONCE(rnp != rdp->mynode);
|
|
|
|
/*
|
|
* Move tasks up to root rcu_node. Don't try to get fancy for
|
|
* this corner-case operation -- just put this node's tasks
|
|
* at the head of the root node's list, and update the root node's
|
|
* ->gp_tasks and ->exp_tasks pointers to those of this node's,
|
|
* if non-NULL. This might result in waiting for more tasks than
|
|
* absolutely necessary, but this is a good performance/complexity
|
|
* tradeoff.
|
|
*/
|
|
if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
|
|
retval |= RCU_OFL_TASKS_NORM_GP;
|
|
if (rcu_preempted_readers_exp(rnp))
|
|
retval |= RCU_OFL_TASKS_EXP_GP;
|
|
lp = &rnp->blkd_tasks;
|
|
lp_root = &rnp_root->blkd_tasks;
|
|
while (!list_empty(lp)) {
|
|
t = list_entry(lp->next, typeof(*t), rcu_node_entry);
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
list_del(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = rnp_root;
|
|
list_add(&t->rcu_node_entry, lp_root);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
rnp_root->gp_tasks = rnp->gp_tasks;
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
rnp_root->exp_tasks = rnp->exp_tasks;
|
|
#ifdef CONFIG_RCU_BOOST
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
rnp_root->boost_tasks = rnp->boost_tasks;
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
}
|
|
|
|
rnp->gp_tasks = NULL;
|
|
rnp->exp_tasks = NULL;
|
|
#ifdef CONFIG_RCU_BOOST
|
|
rnp->boost_tasks = NULL;
|
|
/*
|
|
* In case root is being boosted and leaf was not. Make sure
|
|
* that we boost the tasks blocking the current grace period
|
|
* in this case.
|
|
*/
|
|
raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
|
|
if (rnp_root->boost_tasks != NULL &&
|
|
rnp_root->boost_tasks != rnp_root->gp_tasks &&
|
|
rnp_root->boost_tasks != rnp_root->exp_tasks)
|
|
rnp_root->boost_tasks = rnp_root->gp_tasks;
|
|
raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
return retval;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU. When a task blocks,
|
|
* the task is recorded in the corresponding CPU's rcu_node structure,
|
|
* which is checked elsewhere.
|
|
*
|
|
* Caller must disable hard irqs.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0) {
|
|
rcu_preempt_qs(cpu);
|
|
return;
|
|
}
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
per_cpu(rcu_preempt_data, cpu).qs_pending)
|
|
t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_preempt_do_callbacks(void)
|
|
{
|
|
rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/*
|
|
* Queue a preemptible-RCU callback for invocation after a grace period.
|
|
*/
|
|
void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_preempt_state, -1, 0);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
/*
|
|
* Queue an RCU callback for lazy invocation after a grace period.
|
|
* This will likely be later named something like "call_rcu_lazy()",
|
|
* but this change will require some way of tagging the lazy RCU
|
|
* callbacks in the list of pending callbacks. Until then, this
|
|
* function may only be called from __kfree_rcu().
|
|
*/
|
|
void kfree_call_rcu(struct rcu_head *head,
|
|
void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_preempt_state, -1, 1);
|
|
}
|
|
EXPORT_SYMBOL_GPL(kfree_call_rcu);
|
|
|
|
/**
|
|
* synchronize_rcu - wait until a grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full grace
|
|
* period has elapsed, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. Note, however, that
|
|
* upon return from synchronize_rcu(), the caller might well be executing
|
|
* concurrently with new RCU read-side critical sections that began while
|
|
* synchronize_rcu() was waiting. RCU read-side critical sections are
|
|
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
|
|
*
|
|
* See the description of synchronize_sched() for more detailed information
|
|
* on memory ordering guarantees.
|
|
*/
|
|
void synchronize_rcu(void)
|
|
{
|
|
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
|
|
!lock_is_held(&rcu_lock_map) &&
|
|
!lock_is_held(&rcu_sched_lock_map),
|
|
"Illegal synchronize_rcu() in RCU read-side critical section");
|
|
if (!rcu_scheduler_active)
|
|
return;
|
|
if (rcu_expedited)
|
|
synchronize_rcu_expedited();
|
|
else
|
|
wait_rcu_gp(call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
|
|
|
static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
|
|
static unsigned long sync_rcu_preempt_exp_count;
|
|
static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
|
|
|
|
/*
|
|
* Return non-zero if there are any tasks in RCU read-side critical
|
|
* sections blocking the current preemptible-RCU expedited grace period.
|
|
* If there is no preemptible-RCU expedited grace period currently in
|
|
* progress, returns zero unconditionally.
|
|
*/
|
|
static int rcu_preempted_readers_exp(struct rcu_node *rnp)
|
|
{
|
|
return rnp->exp_tasks != NULL;
|
|
}
|
|
|
|
/*
|
|
* return non-zero if there is no RCU expedited grace period in progress
|
|
* for the specified rcu_node structure, in other words, if all CPUs and
|
|
* tasks covered by the specified rcu_node structure have done their bit
|
|
* for the current expedited grace period. Works only for preemptible
|
|
* RCU -- other RCU implementation use other means.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
|
|
{
|
|
return !rcu_preempted_readers_exp(rnp) &&
|
|
ACCESS_ONCE(rnp->expmask) == 0;
|
|
}
|
|
|
|
/*
|
|
* Report the exit from RCU read-side critical section for the last task
|
|
* that queued itself during or before the current expedited preemptible-RCU
|
|
* grace period. This event is reported either to the rcu_node structure on
|
|
* which the task was queued or to one of that rcu_node structure's ancestors,
|
|
* recursively up the tree. (Calm down, calm down, we do the recursion
|
|
* iteratively!)
|
|
*
|
|
* Most callers will set the "wake" flag, but the task initiating the
|
|
* expedited grace period need not wake itself.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
unsigned long flags;
|
|
unsigned long mask;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
for (;;) {
|
|
if (!sync_rcu_preempt_exp_done(rnp)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
break;
|
|
}
|
|
if (rnp->parent == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
if (wake)
|
|
wake_up(&sync_rcu_preempt_exp_wq);
|
|
break;
|
|
}
|
|
mask = rnp->grpmask;
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
|
|
rnp = rnp->parent;
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled */
|
|
rnp->expmask &= ~mask;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Snapshot the tasks blocking the newly started preemptible-RCU expedited
|
|
* grace period for the specified rcu_node structure. If there are no such
|
|
* tasks, report it up the rcu_node hierarchy.
|
|
*
|
|
* Caller must hold sync_rcu_preempt_exp_mutex and must exclude
|
|
* CPU hotplug operations.
|
|
*/
|
|
static void
|
|
sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
int must_wait = 0;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
if (list_empty(&rnp->blkd_tasks)) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
} else {
|
|
rnp->exp_tasks = rnp->blkd_tasks.next;
|
|
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
|
|
must_wait = 1;
|
|
}
|
|
if (!must_wait)
|
|
rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
|
|
}
|
|
|
|
/**
|
|
* synchronize_rcu_expedited - Brute-force RCU grace period
|
|
*
|
|
* Wait for an RCU-preempt grace period, but expedite it. The basic
|
|
* idea is to invoke synchronize_sched_expedited() to push all the tasks to
|
|
* the ->blkd_tasks lists and wait for this list to drain. This consumes
|
|
* significant time on all CPUs and is unfriendly to real-time workloads,
|
|
* so is thus not recommended for any sort of common-case code.
|
|
* In fact, if you are using synchronize_rcu_expedited() in a loop,
|
|
* please restructure your code to batch your updates, and then Use a
|
|
* single synchronize_rcu() instead.
|
|
*
|
|
* Note that it is illegal to call this function while holding any lock
|
|
* that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
|
|
* to call this function from a CPU-hotplug notifier. Failing to observe
|
|
* these restriction will result in deadlock.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp = &rcu_preempt_state;
|
|
unsigned long snap;
|
|
int trycount = 0;
|
|
|
|
smp_mb(); /* Caller's modifications seen first by other CPUs. */
|
|
snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
|
|
smp_mb(); /* Above access cannot bleed into critical section. */
|
|
|
|
/*
|
|
* Block CPU-hotplug operations. This means that any CPU-hotplug
|
|
* operation that finds an rcu_node structure with tasks in the
|
|
* process of being boosted will know that all tasks blocking
|
|
* this expedited grace period will already be in the process of
|
|
* being boosted. This simplifies the process of moving tasks
|
|
* from leaf to root rcu_node structures.
|
|
*/
|
|
get_online_cpus();
|
|
|
|
/*
|
|
* Acquire lock, falling back to synchronize_rcu() if too many
|
|
* lock-acquisition failures. Of course, if someone does the
|
|
* expedited grace period for us, just leave.
|
|
*/
|
|
while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
|
|
if (ULONG_CMP_LT(snap,
|
|
ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
|
|
put_online_cpus();
|
|
goto mb_ret; /* Others did our work for us. */
|
|
}
|
|
if (trycount++ < 10) {
|
|
udelay(trycount * num_online_cpus());
|
|
} else {
|
|
put_online_cpus();
|
|
wait_rcu_gp(call_rcu);
|
|
return;
|
|
}
|
|
}
|
|
if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
|
|
put_online_cpus();
|
|
goto unlock_mb_ret; /* Others did our work for us. */
|
|
}
|
|
|
|
/* force all RCU readers onto ->blkd_tasks lists. */
|
|
synchronize_sched_expedited();
|
|
|
|
/* Initialize ->expmask for all non-leaf rcu_node structures. */
|
|
rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->expmask = rnp->qsmaskinit;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
/* Snapshot current state of ->blkd_tasks lists. */
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
sync_rcu_preempt_exp_init(rsp, rnp);
|
|
if (NUM_RCU_NODES > 1)
|
|
sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
|
|
|
|
put_online_cpus();
|
|
|
|
/* Wait for snapshotted ->blkd_tasks lists to drain. */
|
|
rnp = rcu_get_root(rsp);
|
|
wait_event(sync_rcu_preempt_exp_wq,
|
|
sync_rcu_preempt_exp_done(rnp));
|
|
|
|
/* Clean up and exit. */
|
|
smp_mb(); /* ensure expedited GP seen before counter increment. */
|
|
ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
|
|
unlock_mb_ret:
|
|
mutex_unlock(&sync_rcu_preempt_exp_mutex);
|
|
mb_ret:
|
|
smp_mb(); /* ensure subsequent action seen after grace period. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
/**
|
|
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
|
*
|
|
* Note that this primitive does not necessarily wait for an RCU grace period
|
|
* to complete. For example, if there are no RCU callbacks queued anywhere
|
|
* in the system, then rcu_barrier() is within its rights to return
|
|
* immediately, without waiting for anything, much less an RCU grace period.
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
_rcu_barrier(&rcu_preempt_state);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Initialize preemptible RCU's state structures.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible-RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings,
|
|
* as debug_check_no_locks_held() already does this if lockdep
|
|
* is enabled.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (likely(list_empty(¤t->rcu_node_entry)))
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
barrier();
|
|
t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
static struct rcu_state *rcu_state = &rcu_sched_state;
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
pr_info("Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Return the number of RCU batches processed thus far for debug & stats.
|
|
*/
|
|
long rcu_batches_completed(void)
|
|
{
|
|
return rcu_batches_completed_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_batches_completed);
|
|
|
|
/*
|
|
* Force a quiescent state for RCU, which, because there is no preemptible
|
|
* RCU, becomes the same as rcu-sched.
|
|
*/
|
|
void rcu_force_quiescent_state(void)
|
|
{
|
|
rcu_sched_force_quiescent_state();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* CPUs being in quiescent states.
|
|
*/
|
|
static void rcu_preempt_note_context_switch(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/* Because preemptible RCU does not exist, no quieting of tasks. */
|
|
static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never needs to migrate
|
|
* tasks that were blocked within RCU read-side critical sections, and
|
|
* such non-existent tasks cannot possibly have been blocking the current
|
|
* grace period.
|
|
*/
|
|
static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
|
|
struct rcu_node *rnp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Queue an RCU callback for lazy invocation after a grace period.
|
|
* This will likely be later named something like "call_rcu_lazy()",
|
|
* but this change will require some way of tagging the lazy RCU
|
|
* callbacks in the list of pending callbacks. Until then, this
|
|
* function may only be called from __kfree_rcu().
|
|
*
|
|
* Because there is no preemptible RCU, we use RCU-sched instead.
|
|
*/
|
|
void kfree_call_rcu(struct rcu_head *head,
|
|
void (*func)(struct rcu_head *rcu))
|
|
{
|
|
__call_rcu(head, func, &rcu_sched_state, -1, 1);
|
|
}
|
|
EXPORT_SYMBOL_GPL(kfree_call_rcu);
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but make it happen quickly.
|
|
* But because preemptible RCU does not exist, map to rcu-sched.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
synchronize_sched_expedited();
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
#ifdef CONFIG_HOTPLUG_CPU
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there is never any need to
|
|
* report on tasks preempted in RCU read-side critical sections during
|
|
* expedited RCU grace periods.
|
|
*/
|
|
static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
|
|
bool wake)
|
|
{
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, rcu_barrier() is just
|
|
* another name for rcu_barrier_sched().
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
rcu_barrier_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it need not be initialized.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
|
* while in preemptible RCU read-side critical sections.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
#include "rtmutex_common.h"
|
|
|
|
#ifdef CONFIG_RCU_TRACE
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
if (list_empty(&rnp->blkd_tasks))
|
|
rnp->n_balk_blkd_tasks++;
|
|
else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
|
|
rnp->n_balk_boost_tasks++;
|
|
else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
|
|
rnp->n_balk_notblocked++;
|
|
else if (rnp->gp_tasks != NULL &&
|
|
ULONG_CMP_LT(jiffies, rnp->boost_time))
|
|
rnp->n_balk_notyet++;
|
|
else
|
|
rnp->n_balk_nos++;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static void rcu_initiate_boost_trace(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_TRACE */
|
|
|
|
static void rcu_wake_cond(struct task_struct *t, int status)
|
|
{
|
|
/*
|
|
* If the thread is yielding, only wake it when this
|
|
* is invoked from idle
|
|
*/
|
|
if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
|
|
wake_up_process(t);
|
|
}
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct rt_mutex mtx;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL) {
|
|
tb = rnp->exp_tasks;
|
|
rnp->n_exp_boosts++;
|
|
} else {
|
|
tb = rnp->boost_tasks;
|
|
rnp->n_normal_boosts++;
|
|
}
|
|
rnp->n_tasks_boosted++;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&mtx, t);
|
|
t->rcu_boost_mutex = &mtx;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
|
|
rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
|
|
|
|
return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
|
|
ACCESS_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread. One per leaf rcu_node and one for the
|
|
* root rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization(TPS("Start boost kthread@init"));
|
|
for (;;) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
|
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
|
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization(TPS("End boost kthread@notreached"));
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases.
|
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
|
* about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
rnp->n_balk_exp_gp_tasks++;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
rnp->boost_tasks = rnp->gp_tasks;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
t = rnp->boost_kthread_task;
|
|
if (t)
|
|
rcu_wake_cond(t, rnp->boost_kthread_status);
|
|
} else {
|
|
rcu_initiate_boost_trace(rnp);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Wake up the per-CPU kthread to invoke RCU callbacks.
|
|
*/
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
__this_cpu_write(rcu_cpu_has_work, 1);
|
|
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
|
|
current != __this_cpu_read(rcu_cpu_kthread_task)) {
|
|
rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
|
|
__this_cpu_read(rcu_cpu_kthread_status));
|
|
}
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return __get_cpu_var(rcu_cpu_kthread_task) == current;
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp)
|
|
{
|
|
int rnp_index = rnp - &rsp->node[0];
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (&rcu_preempt_state != rsp)
|
|
return 0;
|
|
|
|
if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
|
|
return 0;
|
|
|
|
rsp->boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return 0;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
sp.sched_priority = RCU_BOOST_PRIO;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
static void rcu_kthread_do_work(void)
|
|
{
|
|
rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
|
|
rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
|
|
rcu_preempt_do_callbacks();
|
|
}
|
|
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = RCU_KTHREAD_PRIO;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
}
|
|
|
|
static void rcu_cpu_kthread_park(unsigned int cpu)
|
|
{
|
|
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
|
}
|
|
|
|
static int rcu_cpu_kthread_should_run(unsigned int cpu)
|
|
{
|
|
return __get_cpu_var(rcu_cpu_has_work);
|
|
}
|
|
|
|
/*
|
|
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
|
|
* RCU softirq used in flavors and configurations of RCU that do not
|
|
* support RCU priority boosting.
|
|
*/
|
|
static void rcu_cpu_kthread(unsigned int cpu)
|
|
{
|
|
unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status);
|
|
char work, *workp = &__get_cpu_var(rcu_cpu_has_work);
|
|
int spincnt;
|
|
|
|
for (spincnt = 0; spincnt < 10; spincnt++) {
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
|
|
local_bh_disable();
|
|
*statusp = RCU_KTHREAD_RUNNING;
|
|
this_cpu_inc(rcu_cpu_kthread_loops);
|
|
local_irq_disable();
|
|
work = *workp;
|
|
*workp = 0;
|
|
local_irq_enable();
|
|
if (work)
|
|
rcu_kthread_do_work();
|
|
local_bh_enable();
|
|
if (*workp == 0) {
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
return;
|
|
}
|
|
}
|
|
*statusp = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask = rnp->qsmaskinit;
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
|
|
if ((mask & 0x1) && cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0) {
|
|
cpumask_setall(cm);
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
|
|
cpumask_clear_cpu(cpu, cm);
|
|
WARN_ON_ONCE(cpumask_weight(cm) == 0);
|
|
}
|
|
set_cpus_allowed_ptr(t, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
|
|
.store = &rcu_cpu_kthread_task,
|
|
.thread_should_run = rcu_cpu_kthread_should_run,
|
|
.thread_fn = rcu_cpu_kthread,
|
|
.thread_comm = "rcuc/%u",
|
|
.setup = rcu_cpu_kthread_setup,
|
|
.park = rcu_cpu_kthread_park,
|
|
};
|
|
|
|
/*
|
|
* Spawn all kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static int __init rcu_spawn_kthreads(void)
|
|
{
|
|
struct rcu_node *rnp;
|
|
int cpu;
|
|
|
|
rcu_scheduler_fully_active = 1;
|
|
for_each_possible_cpu(cpu)
|
|
per_cpu(rcu_cpu_has_work, cpu) = 0;
|
|
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
|
|
rnp = rcu_get_root(rcu_state);
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
if (NUM_RCU_NODES > 1) {
|
|
rcu_for_each_leaf_node(rcu_state, rnp)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
}
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_spawn_kthreads);
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
{
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
}
|
|
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static int __init rcu_scheduler_really_started(void)
|
|
{
|
|
rcu_scheduler_fully_active = 1;
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_scheduler_really_started);
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*
|
|
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
|
|
* any flavor of RCU.
|
|
*/
|
|
int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
|
|
{
|
|
*delta_jiffies = ULONG_MAX;
|
|
return rcu_cpu_has_callbacks(cpu, NULL);
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Don't bother keeping a running count of the number of RCU callbacks
|
|
* posted because CONFIG_RCU_FAST_NO_HZ=n.
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
/*
|
|
* This code is invoked when a CPU goes idle, at which point we want
|
|
* to have the CPU do everything required for RCU so that it can enter
|
|
* the energy-efficient dyntick-idle mode. This is handled by a
|
|
* state machine implemented by rcu_prepare_for_idle() below.
|
|
*
|
|
* The following three proprocessor symbols control this state machine:
|
|
*
|
|
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
|
|
* to sleep in dyntick-idle mode with RCU callbacks pending. This
|
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
|
* benchmarkers who might otherwise be tempted to set this to a large
|
|
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
|
|
* system. And if you are -that- concerned about energy efficiency,
|
|
* just power the system down and be done with it!
|
|
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
|
|
* permitted to sleep in dyntick-idle mode with only lazy RCU
|
|
* callbacks pending. Setting this too high can OOM your system.
|
|
*
|
|
* The values below work well in practice. If future workloads require
|
|
* adjustment, they can be converted into kernel config parameters, though
|
|
* making the state machine smarter might be a better option.
|
|
*/
|
|
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
|
|
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
|
|
|
|
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
|
|
module_param(rcu_idle_gp_delay, int, 0644);
|
|
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
|
|
module_param(rcu_idle_lazy_gp_delay, int, 0644);
|
|
|
|
extern int tick_nohz_enabled;
|
|
|
|
/*
|
|
* Try to advance callbacks for all flavors of RCU on the current CPU.
|
|
* Afterwards, if there are any callbacks ready for immediate invocation,
|
|
* return true.
|
|
*/
|
|
static bool rcu_try_advance_all_cbs(void)
|
|
{
|
|
bool cbs_ready = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
rnp = rdp->mynode;
|
|
|
|
/*
|
|
* Don't bother checking unless a grace period has
|
|
* completed since we last checked and there are
|
|
* callbacks not yet ready to invoke.
|
|
*/
|
|
if (rdp->completed != rnp->completed &&
|
|
rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
|
|
note_gp_changes(rsp, rdp);
|
|
|
|
if (cpu_has_callbacks_ready_to_invoke(rdp))
|
|
cbs_ready = true;
|
|
}
|
|
return cbs_ready;
|
|
}
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
|
|
* to invoke. If the CPU has callbacks, try to advance them. Tell the
|
|
* caller to set the timeout based on whether or not there are non-lazy
|
|
* callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
int rcu_needs_cpu(int cpu, unsigned long *dj)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
|
|
/* Snapshot to detect later posting of non-lazy callback. */
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
|
|
/* If no callbacks, RCU doesn't need the CPU. */
|
|
if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
|
|
*dj = ULONG_MAX;
|
|
return 0;
|
|
}
|
|
|
|
/* Attempt to advance callbacks. */
|
|
if (rcu_try_advance_all_cbs()) {
|
|
/* Some ready to invoke, so initiate later invocation. */
|
|
invoke_rcu_core();
|
|
return 1;
|
|
}
|
|
rdtp->last_accelerate = jiffies;
|
|
|
|
/* Request timer delay depending on laziness, and round. */
|
|
if (!rdtp->all_lazy) {
|
|
*dj = round_up(rcu_idle_gp_delay + jiffies,
|
|
rcu_idle_gp_delay) - jiffies;
|
|
} else {
|
|
*dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Prepare a CPU for idle from an RCU perspective. The first major task
|
|
* is to sense whether nohz mode has been enabled or disabled via sysfs.
|
|
* The second major task is to check to see if a non-lazy callback has
|
|
* arrived at a CPU that previously had only lazy callbacks. The third
|
|
* major task is to accelerate (that is, assign grace-period numbers to)
|
|
* any recently arrived callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(int cpu)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
int tne;
|
|
|
|
/* Handle nohz enablement switches conservatively. */
|
|
tne = ACCESS_ONCE(tick_nohz_enabled);
|
|
if (tne != rdtp->tick_nohz_enabled_snap) {
|
|
if (rcu_cpu_has_callbacks(cpu, NULL))
|
|
invoke_rcu_core(); /* force nohz to see update. */
|
|
rdtp->tick_nohz_enabled_snap = tne;
|
|
return;
|
|
}
|
|
if (!tne)
|
|
return;
|
|
|
|
/* If this is a no-CBs CPU, no callbacks, just return. */
|
|
if (rcu_is_nocb_cpu(cpu))
|
|
return;
|
|
|
|
/*
|
|
* If a non-lazy callback arrived at a CPU having only lazy
|
|
* callbacks, invoke RCU core for the side-effect of recalculating
|
|
* idle duration on re-entry to idle.
|
|
*/
|
|
if (rdtp->all_lazy &&
|
|
rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
|
|
invoke_rcu_core();
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If we have not yet accelerated this jiffy, accelerate all
|
|
* callbacks on this CPU.
|
|
*/
|
|
if (rdtp->last_accelerate == jiffies)
|
|
return;
|
|
rdtp->last_accelerate = jiffies;
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
if (!*rdp->nxttail[RCU_DONE_TAIL])
|
|
continue;
|
|
rnp = rdp->mynode;
|
|
raw_spin_lock(&rnp->lock); /* irqs already disabled. */
|
|
rcu_accelerate_cbs(rsp, rnp, rdp);
|
|
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
|
* any grace periods that elapsed while the CPU was idle, and if any
|
|
* callbacks are now ready to invoke, initiate invocation.
|
|
*/
|
|
static void rcu_cleanup_after_idle(int cpu)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_state *rsp;
|
|
|
|
if (rcu_is_nocb_cpu(cpu))
|
|
return;
|
|
rcu_try_advance_all_cbs();
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
if (cpu_has_callbacks_ready_to_invoke(rdp))
|
|
invoke_rcu_core();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Keep a running count of the number of non-lazy callbacks posted
|
|
* on this CPU. This running counter (which is never decremented) allows
|
|
* rcu_prepare_for_idle() to detect when something out of the idle loop
|
|
* posts a callback, even if an equal number of callbacks are invoked.
|
|
* Of course, callbacks should only be posted from within a trace event
|
|
* designed to be called from idle or from within RCU_NONIDLE().
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
|
|
}
|
|
|
|
/*
|
|
* Data for flushing lazy RCU callbacks at OOM time.
|
|
*/
|
|
static atomic_t oom_callback_count;
|
|
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
|
|
|
|
/*
|
|
* RCU OOM callback -- decrement the outstanding count and deliver the
|
|
* wake-up if we are the last one.
|
|
*/
|
|
static void rcu_oom_callback(struct rcu_head *rhp)
|
|
{
|
|
if (atomic_dec_and_test(&oom_callback_count))
|
|
wake_up(&oom_callback_wq);
|
|
}
|
|
|
|
/*
|
|
* Post an rcu_oom_notify callback on the current CPU if it has at
|
|
* least one lazy callback. This will unnecessarily post callbacks
|
|
* to CPUs that already have a non-lazy callback at the end of their
|
|
* callback list, but this is an infrequent operation, so accept some
|
|
* extra overhead to keep things simple.
|
|
*/
|
|
static void rcu_oom_notify_cpu(void *unused)
|
|
{
|
|
struct rcu_state *rsp;
|
|
struct rcu_data *rdp;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = __this_cpu_ptr(rsp->rda);
|
|
if (rdp->qlen_lazy != 0) {
|
|
atomic_inc(&oom_callback_count);
|
|
rsp->call(&rdp->oom_head, rcu_oom_callback);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If low on memory, ensure that each CPU has a non-lazy callback.
|
|
* This will wake up CPUs that have only lazy callbacks, in turn
|
|
* ensuring that they free up the corresponding memory in a timely manner.
|
|
* Because an uncertain amount of memory will be freed in some uncertain
|
|
* timeframe, we do not claim to have freed anything.
|
|
*/
|
|
static int rcu_oom_notify(struct notifier_block *self,
|
|
unsigned long notused, void *nfreed)
|
|
{
|
|
int cpu;
|
|
|
|
/* Wait for callbacks from earlier instance to complete. */
|
|
wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
|
|
|
|
/*
|
|
* Prevent premature wakeup: ensure that all increments happen
|
|
* before there is a chance of the counter reaching zero.
|
|
*/
|
|
atomic_set(&oom_callback_count, 1);
|
|
|
|
get_online_cpus();
|
|
for_each_online_cpu(cpu) {
|
|
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
|
|
cond_resched();
|
|
}
|
|
put_online_cpus();
|
|
|
|
/* Unconditionally decrement: no need to wake ourselves up. */
|
|
atomic_dec(&oom_callback_count);
|
|
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block rcu_oom_nb = {
|
|
.notifier_call = rcu_oom_notify
|
|
};
|
|
|
|
static int __init rcu_register_oom_notifier(void)
|
|
{
|
|
register_oom_notifier(&rcu_oom_nb);
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_register_oom_notifier);
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#ifdef CONFIG_RCU_CPU_STALL_INFO
|
|
|
|
#ifdef CONFIG_RCU_FAST_NO_HZ
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
|
|
|
|
sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
|
|
rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
|
|
ulong2long(nlpd),
|
|
rdtp->all_lazy ? 'L' : '.',
|
|
rdtp->tick_nohz_enabled_snap ? '.' : 'D');
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
*cp = '\0';
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
/* Initiate the stall-info list. */
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
/*
|
|
* Print out diagnostic information for the specified stalled CPU.
|
|
*
|
|
* If the specified CPU is aware of the current RCU grace period
|
|
* (flavor specified by rsp), then print the number of scheduling
|
|
* clock interrupts the CPU has taken during the time that it has
|
|
* been aware. Otherwise, print the number of RCU grace periods
|
|
* that this CPU is ignorant of, for example, "1" if the CPU was
|
|
* aware of the previous grace period.
|
|
*
|
|
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
|
|
*/
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
char fast_no_hz[72];
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
struct rcu_dynticks *rdtp = rdp->dynticks;
|
|
char *ticks_title;
|
|
unsigned long ticks_value;
|
|
|
|
if (rsp->gpnum == rdp->gpnum) {
|
|
ticks_title = "ticks this GP";
|
|
ticks_value = rdp->ticks_this_gp;
|
|
} else {
|
|
ticks_title = "GPs behind";
|
|
ticks_value = rsp->gpnum - rdp->gpnum;
|
|
}
|
|
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
|
|
pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
|
|
cpu, ticks_value, ticks_title,
|
|
atomic_read(&rdtp->dynticks) & 0xfff,
|
|
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
|
|
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
|
|
fast_no_hz);
|
|
}
|
|
|
|
/* Terminate the stall-info list. */
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
pr_err("\t");
|
|
}
|
|
|
|
/* Zero ->ticks_this_gp for all flavors of RCU. */
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
rdp->ticks_this_gp = 0;
|
|
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
|
|
}
|
|
|
|
/* Increment ->ticks_this_gp for all flavors of RCU. */
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
for_each_rcu_flavor(rsp)
|
|
__this_cpu_ptr(rsp->rda)->ticks_this_gp++;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
pr_cont(" {");
|
|
}
|
|
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
pr_cont(" %d", cpu);
|
|
}
|
|
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
pr_cont("} ");
|
|
}
|
|
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
|
|
/*
|
|
* Offload callback processing from the boot-time-specified set of CPUs
|
|
* specified by rcu_nocb_mask. For each CPU in the set, there is a
|
|
* kthread created that pulls the callbacks from the corresponding CPU,
|
|
* waits for a grace period to elapse, and invokes the callbacks.
|
|
* The no-CBs CPUs do a wake_up() on their kthread when they insert
|
|
* a callback into any empty list, unless the rcu_nocb_poll boot parameter
|
|
* has been specified, in which case each kthread actively polls its
|
|
* CPU. (Which isn't so great for energy efficiency, but which does
|
|
* reduce RCU's overhead on that CPU.)
|
|
*
|
|
* This is intended to be used in conjunction with Frederic Weisbecker's
|
|
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
|
|
* running CPU-bound user-mode computations.
|
|
*
|
|
* Offloading of callback processing could also in theory be used as
|
|
* an energy-efficiency measure because CPUs with no RCU callbacks
|
|
* queued are more aggressive about entering dyntick-idle mode.
|
|
*/
|
|
|
|
|
|
/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
|
|
static int __init rcu_nocb_setup(char *str)
|
|
{
|
|
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
|
|
have_rcu_nocb_mask = true;
|
|
cpulist_parse(str, rcu_nocb_mask);
|
|
return 1;
|
|
}
|
|
__setup("rcu_nocbs=", rcu_nocb_setup);
|
|
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
|
{
|
|
rcu_nocb_poll = 1;
|
|
return 0;
|
|
}
|
|
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
|
|
|
|
/*
|
|
* Do any no-CBs CPUs need another grace period?
|
|
*
|
|
* Interrupts must be disabled. If the caller does not hold the root
|
|
* rnp_node structure's ->lock, the results are advisory only.
|
|
*/
|
|
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
|
|
}
|
|
|
|
/*
|
|
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
|
|
* grace period.
|
|
*/
|
|
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
|
|
{
|
|
wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
|
|
}
|
|
|
|
/*
|
|
* Set the root rcu_node structure's ->need_future_gp field
|
|
* based on the sum of those of all rcu_node structures. This does
|
|
* double-count the root rcu_node structure's requests, but this
|
|
* is necessary to handle the possibility of a rcu_nocb_kthread()
|
|
* having awakened during the time that the rcu_node structures
|
|
* were being updated for the end of the previous grace period.
|
|
*/
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
init_waitqueue_head(&rnp->nocb_gp_wq[0]);
|
|
init_waitqueue_head(&rnp->nocb_gp_wq[1]);
|
|
}
|
|
|
|
/* Is the specified CPU a no-CPUs CPU? */
|
|
bool rcu_is_nocb_cpu(int cpu)
|
|
{
|
|
if (have_rcu_nocb_mask)
|
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Enqueue the specified string of rcu_head structures onto the specified
|
|
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
|
|
* string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
|
|
* counts are supplied by rhcount and rhcount_lazy.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
|
|
struct rcu_head *rhp,
|
|
struct rcu_head **rhtp,
|
|
int rhcount, int rhcount_lazy)
|
|
{
|
|
int len;
|
|
struct rcu_head **old_rhpp;
|
|
struct task_struct *t;
|
|
|
|
/* Enqueue the callback on the nocb list and update counts. */
|
|
old_rhpp = xchg(&rdp->nocb_tail, rhtp);
|
|
ACCESS_ONCE(*old_rhpp) = rhp;
|
|
atomic_long_add(rhcount, &rdp->nocb_q_count);
|
|
atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
|
|
|
|
/* If we are not being polled and there is a kthread, awaken it ... */
|
|
t = ACCESS_ONCE(rdp->nocb_kthread);
|
|
if (rcu_nocb_poll | !t)
|
|
return;
|
|
len = atomic_long_read(&rdp->nocb_q_count);
|
|
if (old_rhpp == &rdp->nocb_head) {
|
|
wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
|
|
rdp->qlen_last_fqs_check = 0;
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
wake_up_process(t); /* ... or if many callbacks queued. */
|
|
rdp->qlen_last_fqs_check = LONG_MAX / 2;
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* This is a helper for __call_rcu(), which invokes this when the normal
|
|
* callback queue is inoperable. If this is not a no-CBs CPU, this
|
|
* function returns failure back to __call_rcu(), which can complain
|
|
* appropriately.
|
|
*
|
|
* Otherwise, this function queues the callback where the corresponding
|
|
* "rcuo" kthread can find it.
|
|
*/
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy)
|
|
{
|
|
|
|
if (!rcu_is_nocb_cpu(rdp->cpu))
|
|
return 0;
|
|
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
|
|
if (__is_kfree_rcu_offset((unsigned long)rhp->func))
|
|
trace_rcu_kfree_callback(rdp->rsp->name, rhp,
|
|
(unsigned long)rhp->func,
|
|
rdp->qlen_lazy, rdp->qlen);
|
|
else
|
|
trace_rcu_callback(rdp->rsp->name, rhp,
|
|
rdp->qlen_lazy, rdp->qlen);
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
|
|
* not a no-CBs CPU.
|
|
*/
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
long ql = rsp->qlen;
|
|
long qll = rsp->qlen_lazy;
|
|
|
|
/* If this is not a no-CBs CPU, tell the caller to do it the old way. */
|
|
if (!rcu_is_nocb_cpu(smp_processor_id()))
|
|
return 0;
|
|
rsp->qlen = 0;
|
|
rsp->qlen_lazy = 0;
|
|
|
|
/* First, enqueue the donelist, if any. This preserves CB ordering. */
|
|
if (rsp->orphan_donelist != NULL) {
|
|
__call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
|
|
rsp->orphan_donetail, ql, qll);
|
|
ql = qll = 0;
|
|
rsp->orphan_donelist = NULL;
|
|
rsp->orphan_donetail = &rsp->orphan_donelist;
|
|
}
|
|
if (rsp->orphan_nxtlist != NULL) {
|
|
__call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
|
|
rsp->orphan_nxttail, ql, qll);
|
|
ql = qll = 0;
|
|
rsp->orphan_nxtlist = NULL;
|
|
rsp->orphan_nxttail = &rsp->orphan_nxtlist;
|
|
}
|
|
return 1;
|
|
}
|
|
|
|
/*
|
|
* If necessary, kick off a new grace period, and either way wait
|
|
* for a subsequent grace period to complete.
|
|
*/
|
|
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
|
|
{
|
|
unsigned long c;
|
|
bool d;
|
|
unsigned long flags;
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
raw_spin_lock_irqsave(&rnp->lock, flags);
|
|
c = rcu_start_future_gp(rnp, rdp);
|
|
raw_spin_unlock_irqrestore(&rnp->lock, flags);
|
|
|
|
/*
|
|
* Wait for the grace period. Do so interruptibly to avoid messing
|
|
* up the load average.
|
|
*/
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
|
|
for (;;) {
|
|
wait_event_interruptible(
|
|
rnp->nocb_gp_wq[c & 0x1],
|
|
(d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
|
|
if (likely(d))
|
|
break;
|
|
flush_signals(current);
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
|
|
}
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
|
|
smp_mb(); /* Ensure that CB invocation happens after GP end. */
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
|
|
* callbacks queued by the corresponding no-CBs CPU.
|
|
*/
|
|
static int rcu_nocb_kthread(void *arg)
|
|
{
|
|
int c, cl;
|
|
struct rcu_head *list;
|
|
struct rcu_head *next;
|
|
struct rcu_head **tail;
|
|
struct rcu_data *rdp = arg;
|
|
|
|
/* Each pass through this loop invokes one batch of callbacks */
|
|
for (;;) {
|
|
/* If not polling, wait for next batch of callbacks. */
|
|
if (!rcu_nocb_poll)
|
|
wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
|
|
list = ACCESS_ONCE(rdp->nocb_head);
|
|
if (!list) {
|
|
schedule_timeout_interruptible(1);
|
|
flush_signals(current);
|
|
continue;
|
|
}
|
|
|
|
/*
|
|
* Extract queued callbacks, update counts, and wait
|
|
* for a grace period to elapse.
|
|
*/
|
|
ACCESS_ONCE(rdp->nocb_head) = NULL;
|
|
tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
|
|
c = atomic_long_xchg(&rdp->nocb_q_count, 0);
|
|
cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
|
|
ACCESS_ONCE(rdp->nocb_p_count) += c;
|
|
ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
|
|
rcu_nocb_wait_gp(rdp);
|
|
|
|
/* Each pass through the following loop invokes a callback. */
|
|
trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
|
|
c = cl = 0;
|
|
while (list) {
|
|
next = list->next;
|
|
/* Wait for enqueuing to complete, if needed. */
|
|
while (next == NULL && &list->next != tail) {
|
|
schedule_timeout_interruptible(1);
|
|
next = list->next;
|
|
}
|
|
debug_rcu_head_unqueue(list);
|
|
local_bh_disable();
|
|
if (__rcu_reclaim(rdp->rsp->name, list))
|
|
cl++;
|
|
c++;
|
|
local_bh_enable();
|
|
list = next;
|
|
}
|
|
trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
|
|
ACCESS_ONCE(rdp->nocb_p_count) -= c;
|
|
ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
|
|
rdp->n_nocbs_invoked += c;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
rdp->nocb_tail = &rdp->nocb_head;
|
|
init_waitqueue_head(&rdp->nocb_wq);
|
|
}
|
|
|
|
/* Create a kthread for each RCU flavor for each no-CBs CPU. */
|
|
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
int cpu;
|
|
struct rcu_data *rdp;
|
|
struct task_struct *t;
|
|
|
|
if (rcu_nocb_mask == NULL)
|
|
return;
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
t = kthread_run(rcu_nocb_kthread, rdp,
|
|
"rcuo%c/%d", rsp->abbr, cpu);
|
|
BUG_ON(IS_ERR(t));
|
|
ACCESS_ONCE(rdp->nocb_kthread) = t;
|
|
}
|
|
}
|
|
|
|
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
if (rcu_nocb_mask == NULL ||
|
|
!cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
|
|
return false;
|
|
rdp->nxttail[RCU_NEXT_TAIL] = NULL;
|
|
return true;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
static int rcu_nocb_needs_gp(struct rcu_state *rsp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
|
|
struct rcu_data *rdp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/*
|
|
* An adaptive-ticks CPU can potentially execute in kernel mode for an
|
|
* arbitrarily long period of time with the scheduling-clock tick turned
|
|
* off. RCU will be paying attention to this CPU because it is in the
|
|
* kernel, but the CPU cannot be guaranteed to be executing the RCU state
|
|
* machine because the scheduling-clock tick has been disabled. Therefore,
|
|
* if an adaptive-ticks CPU is failing to respond to the current grace
|
|
* period and has not be idle from an RCU perspective, kick it.
|
|
*/
|
|
static void rcu_kick_nohz_cpu(int cpu)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(cpu))
|
|
smp_send_reschedule(cpu);
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
}
|
|
|
|
|
|
#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
|
|
|
|
/*
|
|
* Define RCU flavor that holds sysidle state. This needs to be the
|
|
* most active flavor of RCU.
|
|
*/
|
|
#ifdef CONFIG_PREEMPT_RCU
|
|
static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
static int full_sysidle_state; /* Current system-idle state. */
|
|
#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
|
|
#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
|
|
#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
|
|
#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
|
|
#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
|
|
|
|
/*
|
|
* Invoked to note exit from irq or task transition to idle. Note that
|
|
* usermode execution does -not- count as idle here! After all, we want
|
|
* to detect full-system idle states, not RCU quiescent states and grace
|
|
* periods. The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
|
|
{
|
|
unsigned long j;
|
|
|
|
/* Adjust nesting, check for fully idle. */
|
|
if (irq) {
|
|
rdtp->dynticks_idle_nesting--;
|
|
WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
|
|
if (rdtp->dynticks_idle_nesting != 0)
|
|
return; /* Still not fully idle. */
|
|
} else {
|
|
if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
|
|
DYNTICK_TASK_NEST_VALUE) {
|
|
rdtp->dynticks_idle_nesting = 0;
|
|
} else {
|
|
rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
|
|
WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
|
|
return; /* Still not fully idle. */
|
|
}
|
|
}
|
|
|
|
/* Record start of fully idle period. */
|
|
j = jiffies;
|
|
ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
|
|
smp_mb__before_atomic_inc();
|
|
atomic_inc(&rdtp->dynticks_idle);
|
|
smp_mb__after_atomic_inc();
|
|
WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
|
|
}
|
|
|
|
/*
|
|
* Unconditionally force exit from full system-idle state. This is
|
|
* invoked when a normal CPU exits idle, but must be called separately
|
|
* for the timekeeping CPU (tick_do_timer_cpu). The reason for this
|
|
* is that the timekeeping CPU is permitted to take scheduling-clock
|
|
* interrupts while the system is in system-idle state, and of course
|
|
* rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
|
|
* interrupt from any other type of interrupt.
|
|
*/
|
|
void rcu_sysidle_force_exit(void)
|
|
{
|
|
int oldstate = ACCESS_ONCE(full_sysidle_state);
|
|
int newoldstate;
|
|
|
|
/*
|
|
* Each pass through the following loop attempts to exit full
|
|
* system-idle state. If contention proves to be a problem,
|
|
* a trylock-based contention tree could be used here.
|
|
*/
|
|
while (oldstate > RCU_SYSIDLE_SHORT) {
|
|
newoldstate = cmpxchg(&full_sysidle_state,
|
|
oldstate, RCU_SYSIDLE_NOT);
|
|
if (oldstate == newoldstate &&
|
|
oldstate == RCU_SYSIDLE_FULL_NOTED) {
|
|
rcu_kick_nohz_cpu(tick_do_timer_cpu);
|
|
return; /* We cleared it, done! */
|
|
}
|
|
oldstate = newoldstate;
|
|
}
|
|
smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
|
|
}
|
|
|
|
/*
|
|
* Invoked to note entry to irq or task transition from idle. Note that
|
|
* usermode execution does -not- count as idle here! The caller must
|
|
* have disabled interrupts.
|
|
*/
|
|
static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
|
|
{
|
|
/* Adjust nesting, check for already non-idle. */
|
|
if (irq) {
|
|
rdtp->dynticks_idle_nesting++;
|
|
WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
|
|
if (rdtp->dynticks_idle_nesting != 1)
|
|
return; /* Already non-idle. */
|
|
} else {
|
|
/*
|
|
* Allow for irq misnesting. Yes, it really is possible
|
|
* to enter an irq handler then never leave it, and maybe
|
|
* also vice versa. Handle both possibilities.
|
|
*/
|
|
if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
|
|
rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
|
|
WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
|
|
return; /* Already non-idle. */
|
|
} else {
|
|
rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
|
|
}
|
|
}
|
|
|
|
/* Record end of idle period. */
|
|
smp_mb__before_atomic_inc();
|
|
atomic_inc(&rdtp->dynticks_idle);
|
|
smp_mb__after_atomic_inc();
|
|
WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
|
|
|
|
/*
|
|
* If we are the timekeeping CPU, we are permitted to be non-idle
|
|
* during a system-idle state. This must be the case, because
|
|
* the timekeeping CPU has to take scheduling-clock interrupts
|
|
* during the time that the system is transitioning to full
|
|
* system-idle state. This means that the timekeeping CPU must
|
|
* invoke rcu_sysidle_force_exit() directly if it does anything
|
|
* more than take a scheduling-clock interrupt.
|
|
*/
|
|
if (smp_processor_id() == tick_do_timer_cpu)
|
|
return;
|
|
|
|
/* Update system-idle state: We are clearly no longer fully idle! */
|
|
rcu_sysidle_force_exit();
|
|
}
|
|
|
|
/*
|
|
* Check to see if the current CPU is idle. Note that usermode execution
|
|
* does not count as idle. The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
|
|
unsigned long *maxj)
|
|
{
|
|
int cur;
|
|
unsigned long j;
|
|
struct rcu_dynticks *rdtp = rdp->dynticks;
|
|
|
|
/*
|
|
* If some other CPU has already reported non-idle, if this is
|
|
* not the flavor of RCU that tracks sysidle state, or if this
|
|
* is an offline or the timekeeping CPU, nothing to do.
|
|
*/
|
|
if (!*isidle || rdp->rsp != rcu_sysidle_state ||
|
|
cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
|
|
return;
|
|
if (rcu_gp_in_progress(rdp->rsp))
|
|
WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
|
|
|
|
/* Pick up current idle and NMI-nesting counter and check. */
|
|
cur = atomic_read(&rdtp->dynticks_idle);
|
|
if (cur & 0x1) {
|
|
*isidle = false; /* We are not idle! */
|
|
return;
|
|
}
|
|
smp_mb(); /* Read counters before timestamps. */
|
|
|
|
/* Pick up timestamps. */
|
|
j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
|
|
/* If this CPU entered idle more recently, update maxj timestamp. */
|
|
if (ULONG_CMP_LT(*maxj, j))
|
|
*maxj = j;
|
|
}
|
|
|
|
/*
|
|
* Is this the flavor of RCU that is handling full-system idle?
|
|
*/
|
|
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
|
|
{
|
|
return rsp == rcu_sysidle_state;
|
|
}
|
|
|
|
/*
|
|
* Bind the grace-period kthread for the sysidle flavor of RCU to the
|
|
* timekeeping CPU.
|
|
*/
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
int cpu = ACCESS_ONCE(tick_do_timer_cpu);
|
|
|
|
if (cpu < 0 || cpu >= nr_cpu_ids)
|
|
return;
|
|
if (raw_smp_processor_id() != cpu)
|
|
set_cpus_allowed_ptr(current, cpumask_of(cpu));
|
|
}
|
|
|
|
/*
|
|
* Return a delay in jiffies based on the number of CPUs, rcu_node
|
|
* leaf fanout, and jiffies tick rate. The idea is to allow larger
|
|
* systems more time to transition to full-idle state in order to
|
|
* avoid the cache thrashing that otherwise occur on the state variable.
|
|
* Really small systems (less than a couple of tens of CPUs) should
|
|
* instead use a single global atomically incremented counter, and later
|
|
* versions of this will automatically reconfigure themselves accordingly.
|
|
*/
|
|
static unsigned long rcu_sysidle_delay(void)
|
|
{
|
|
if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
|
|
return 0;
|
|
return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
|
|
}
|
|
|
|
/*
|
|
* Advance the full-system-idle state. This is invoked when all of
|
|
* the non-timekeeping CPUs are idle.
|
|
*/
|
|
static void rcu_sysidle(unsigned long j)
|
|
{
|
|
/* Check the current state. */
|
|
switch (ACCESS_ONCE(full_sysidle_state)) {
|
|
case RCU_SYSIDLE_NOT:
|
|
|
|
/* First time all are idle, so note a short idle period. */
|
|
ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
|
|
break;
|
|
|
|
case RCU_SYSIDLE_SHORT:
|
|
|
|
/*
|
|
* Idle for a bit, time to advance to next state?
|
|
* cmpxchg failure means race with non-idle, let them win.
|
|
*/
|
|
if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
|
|
(void)cmpxchg(&full_sysidle_state,
|
|
RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
|
|
break;
|
|
|
|
case RCU_SYSIDLE_LONG:
|
|
|
|
/*
|
|
* Do an additional check pass before advancing to full.
|
|
* cmpxchg failure means race with non-idle, let them win.
|
|
*/
|
|
if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
|
|
(void)cmpxchg(&full_sysidle_state,
|
|
RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
|
|
break;
|
|
|
|
default:
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Found a non-idle non-timekeeping CPU, so kick the system-idle state
|
|
* back to the beginning.
|
|
*/
|
|
static void rcu_sysidle_cancel(void)
|
|
{
|
|
smp_mb();
|
|
ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
|
|
}
|
|
|
|
/*
|
|
* Update the sysidle state based on the results of a force-quiescent-state
|
|
* scan of the CPUs' dyntick-idle state.
|
|
*/
|
|
static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
|
|
unsigned long maxj, bool gpkt)
|
|
{
|
|
if (rsp != rcu_sysidle_state)
|
|
return; /* Wrong flavor, ignore. */
|
|
if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
|
|
return; /* Running state machine from timekeeping CPU. */
|
|
if (isidle)
|
|
rcu_sysidle(maxj); /* More idle! */
|
|
else
|
|
rcu_sysidle_cancel(); /* Idle is over. */
|
|
}
|
|
|
|
/*
|
|
* Wrapper for rcu_sysidle_report() when called from the grace-period
|
|
* kthread's context.
|
|
*/
|
|
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
|
|
unsigned long maxj)
|
|
{
|
|
rcu_sysidle_report(rsp, isidle, maxj, true);
|
|
}
|
|
|
|
/* Callback and function for forcing an RCU grace period. */
|
|
struct rcu_sysidle_head {
|
|
struct rcu_head rh;
|
|
int inuse;
|
|
};
|
|
|
|
static void rcu_sysidle_cb(struct rcu_head *rhp)
|
|
{
|
|
struct rcu_sysidle_head *rshp;
|
|
|
|
/*
|
|
* The following memory barrier is needed to replace the
|
|
* memory barriers that would normally be in the memory
|
|
* allocator.
|
|
*/
|
|
smp_mb(); /* grace period precedes setting inuse. */
|
|
|
|
rshp = container_of(rhp, struct rcu_sysidle_head, rh);
|
|
ACCESS_ONCE(rshp->inuse) = 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if the system is fully idle, other than the timekeeping CPU.
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
bool rcu_sys_is_idle(void)
|
|
{
|
|
static struct rcu_sysidle_head rsh;
|
|
int rss = ACCESS_ONCE(full_sysidle_state);
|
|
|
|
if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
|
|
return false;
|
|
|
|
/* Handle small-system case by doing a full scan of CPUs. */
|
|
if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
|
|
int oldrss = rss - 1;
|
|
|
|
/*
|
|
* One pass to advance to each state up to _FULL.
|
|
* Give up if any pass fails to advance the state.
|
|
*/
|
|
while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
|
|
int cpu;
|
|
bool isidle = true;
|
|
unsigned long maxj = jiffies - ULONG_MAX / 4;
|
|
struct rcu_data *rdp;
|
|
|
|
/* Scan all the CPUs looking for nonidle CPUs. */
|
|
for_each_possible_cpu(cpu) {
|
|
rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
|
|
rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
|
|
if (!isidle)
|
|
break;
|
|
}
|
|
rcu_sysidle_report(rcu_sysidle_state,
|
|
isidle, maxj, false);
|
|
oldrss = rss;
|
|
rss = ACCESS_ONCE(full_sysidle_state);
|
|
}
|
|
}
|
|
|
|
/* If this is the first observation of an idle period, record it. */
|
|
if (rss == RCU_SYSIDLE_FULL) {
|
|
rss = cmpxchg(&full_sysidle_state,
|
|
RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
|
|
return rss == RCU_SYSIDLE_FULL;
|
|
}
|
|
|
|
smp_mb(); /* ensure rss load happens before later caller actions. */
|
|
|
|
/* If already fully idle, tell the caller (in case of races). */
|
|
if (rss == RCU_SYSIDLE_FULL_NOTED)
|
|
return true;
|
|
|
|
/*
|
|
* If we aren't there yet, and a grace period is not in flight,
|
|
* initiate a grace period. Either way, tell the caller that
|
|
* we are not there yet. We use an xchg() rather than an assignment
|
|
* to make up for the memory barriers that would otherwise be
|
|
* provided by the memory allocator.
|
|
*/
|
|
if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
|
|
!rcu_gp_in_progress(rcu_sysidle_state) &&
|
|
!rsh.inuse && xchg(&rsh.inuse, 1) == 0)
|
|
call_rcu(&rsh.rh, rcu_sysidle_cb);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Initialize dynticks sysidle state for CPUs coming online.
|
|
*/
|
|
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
|
|
{
|
|
rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
|
|
|
|
static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
|
|
{
|
|
}
|
|
|
|
static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
|
|
{
|
|
}
|
|
|
|
static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
|
|
unsigned long *maxj)
|
|
{
|
|
}
|
|
|
|
static bool is_sysidle_rcu_state(struct rcu_state *rsp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
}
|
|
|
|
static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
|
|
unsigned long maxj)
|
|
{
|
|
}
|
|
|
|
static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
|