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![Pingfan Liu](/assets/img/avatar_default.png)
Once either rcutree_online_cpu() or rcutree_dead_cpu() is invoked concurrently, the following rcu_boost_kthread_setaffinity() race can occur: CPU 1 CPU2 mask = rcu_rnp_online_cpus(rnp); ... mask = rcu_rnp_online_cpus(rnp); ... set_cpus_allowed_ptr(t, cm); set_cpus_allowed_ptr(t, cm); This results in CPU2's update being overwritten by that of CPU1, and thus the possibility of ->boost_kthread_task continuing to run on a to-be-offlined CPU. This commit therefore eliminates this race by relying on the pre-existing acquisition of ->boost_kthread_mutex to serialize the full process of changing the affinity of ->boost_kthread_task. Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: David Woodhouse <dwmw@amazon.co.uk> Cc: Frederic Weisbecker <frederic@kernel.org> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
1305 lines
42 KiB
C
1305 lines
42 KiB
C
/* SPDX-License-Identifier: GPL-2.0+ */
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/*
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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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* 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.ibm.com>
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*/
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#include "../locking/rtmutex_common.h"
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static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
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{
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/*
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* In order to read the offloaded state of an rdp in a safe
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* and stable way and prevent from its value to be changed
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* under us, we must either hold the barrier mutex, the cpu
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* hotplug lock (read or write) or the nocb lock. Local
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* non-preemptible reads are also safe. NOCB kthreads and
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* timers have their own means of synchronization against the
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* offloaded state updaters.
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*/
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RCU_LOCKDEP_WARN(
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!(lockdep_is_held(&rcu_state.barrier_mutex) ||
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(IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
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rcu_lockdep_is_held_nocb(rdp) ||
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(rdp == this_cpu_ptr(&rcu_data) &&
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!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
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rcu_current_is_nocb_kthread(rdp)),
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"Unsafe read of RCU_NOCB offloaded state"
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);
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return rcu_segcblist_is_offloaded(&rdp->cblist);
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}
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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.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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if (IS_ENABLED(CONFIG_RCU_TRACE))
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pr_info("\tRCU event tracing is enabled.\n");
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if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
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(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
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pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
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RCU_FANOUT);
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if (rcu_fanout_exact)
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pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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if (IS_ENABLED(CONFIG_PROVE_RCU))
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pr_info("\tRCU lockdep checking is enabled.\n");
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if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
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pr_info("\tRCU strict (and thus non-scalable) grace periods are enabled.\n");
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if (RCU_NUM_LVLS >= 4)
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pr_info("\tFour(or more)-level hierarchy is enabled.\n");
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if (RCU_FANOUT_LEAF != 16)
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pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
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RCU_FANOUT_LEAF);
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if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
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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=%u.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
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pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
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kthread_prio, CONFIG_RCU_BOOST_DELAY);
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#endif
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if (blimit != DEFAULT_RCU_BLIMIT)
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pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
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if (qhimark != DEFAULT_RCU_QHIMARK)
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pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
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if (qlowmark != DEFAULT_RCU_QLOMARK)
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pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
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if (qovld != DEFAULT_RCU_QOVLD)
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pr_info("\tBoot-time adjustment of callback overload level to %ld.\n", qovld);
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if (jiffies_till_first_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
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if (jiffies_till_next_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
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if (jiffies_till_sched_qs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
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if (rcu_kick_kthreads)
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pr_info("\tKick kthreads if too-long grace period.\n");
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if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
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pr_info("\tRCU callback double-/use-after-free debug is enabled.\n");
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if (gp_preinit_delay)
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pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
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if (gp_init_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
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if (gp_cleanup_delay)
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pr_info("\tRCU debug GP cleanup slowdown %d jiffies.\n", gp_cleanup_delay);
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if (!use_softirq)
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pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
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if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
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pr_info("\tRCU debug extended QS entry/exit.\n");
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rcupdate_announce_bootup_oddness();
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}
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#ifdef CONFIG_PREEMPT_RCU
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static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
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static void rcu_read_unlock_special(struct task_struct *t);
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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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/* Flags for rcu_preempt_ctxt_queue() decision table. */
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#define RCU_GP_TASKS 0x8
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#define RCU_EXP_TASKS 0x4
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#define RCU_GP_BLKD 0x2
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#define RCU_EXP_BLKD 0x1
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/*
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* Queues a task preempted within an RCU-preempt read-side critical
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* section into the appropriate location within the ->blkd_tasks list,
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* depending on the states of any ongoing normal and expedited grace
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* periods. The ->gp_tasks pointer indicates which element the normal
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* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
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* indicates which element the expedited grace period is waiting on (again,
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* NULL if none). If a grace period is waiting on a given element in the
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* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
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* adding a task to the tail of the list blocks any grace period that is
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* already waiting on one of the elements. In contrast, adding a task
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* to the head of the list won't block any grace period that is already
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* waiting on one of the elements.
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*
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* This queuing is imprecise, and can sometimes make an ongoing grace
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* period wait for a task that is not strictly speaking blocking it.
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* Given the choice, we needlessly block a normal grace period rather than
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* blocking an expedited grace period.
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*
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* Note that an endless sequence of expedited grace periods still cannot
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* indefinitely postpone a normal grace period. Eventually, all of the
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* fixed number of preempted tasks blocking the normal grace period that are
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* not also blocking the expedited grace period will resume and complete
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* their RCU read-side critical sections. At that point, the ->gp_tasks
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* pointer will equal the ->exp_tasks pointer, at which point the end of
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* the corresponding expedited grace period will also be the end of the
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* normal grace period.
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*/
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static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
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__releases(rnp->lock) /* But leaves rrupts disabled. */
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{
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int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
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(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
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(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
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(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
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struct task_struct *t = current;
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raw_lockdep_assert_held_rcu_node(rnp);
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WARN_ON_ONCE(rdp->mynode != rnp);
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WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
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/* RCU better not be waiting on newly onlined CPUs! */
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WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
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rdp->grpmask);
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/*
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* Decide where to queue the newly blocked task. In theory,
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* this could be an if-statement. In practice, when I tried
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* that, it was quite messy.
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*/
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switch (blkd_state) {
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case 0:
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case RCU_EXP_TASKS:
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case RCU_EXP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS:
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case RCU_GP_TASKS + RCU_EXP_TASKS:
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/*
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* Blocking neither GP, or first task blocking the normal
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* GP but not blocking the already-waiting expedited GP.
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* Queue at the head of the list to avoid unnecessarily
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* blocking the already-waiting GPs.
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*/
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_BLKD:
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case RCU_GP_BLKD:
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case RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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/*
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* First task arriving that blocks either GP, or first task
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* arriving that blocks the expedited GP (with the normal
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* GP already waiting), or a task arriving that blocks
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* both GPs with both GPs already waiting. Queue at the
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* tail of the list to avoid any GP waiting on any of the
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* already queued tasks that are not blocking it.
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*/
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list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_TASKS + RCU_EXP_BLKD:
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case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
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/*
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* Second or subsequent task blocking the expedited GP.
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* The task either does not block the normal GP, or is the
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* first task blocking the normal GP. Queue just after
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* the first task blocking the expedited GP.
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*/
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list_add(&t->rcu_node_entry, rnp->exp_tasks);
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break;
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case RCU_GP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
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/*
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* Second or subsequent task blocking the normal GP.
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* The task does not block the expedited GP. Queue just
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* after the first task blocking the normal GP.
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*/
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list_add(&t->rcu_node_entry, rnp->gp_tasks);
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break;
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default:
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/* Yet another exercise in excessive paranoia. */
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WARN_ON_ONCE(1);
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break;
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}
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/*
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* We have now queued the task. If it was the first one to
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* block either grace period, update the ->gp_tasks and/or
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* ->exp_tasks pointers, respectively, to reference the newly
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* blocked tasks.
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*/
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if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
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WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
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WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
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}
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if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
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WRITE_ONCE(rnp->exp_tasks, &t->rcu_node_entry);
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WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
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!(rnp->qsmask & rdp->grpmask));
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WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
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!(rnp->expmask & rdp->grpmask));
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raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
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/*
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* Report the quiescent state for the expedited GP. This expedited
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* GP should not be able to end until we report, so there should be
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* no need to check for a subsequent expedited GP. (Though we are
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* still in a quiescent state in any case.)
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*/
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if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp)
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rcu_report_exp_rdp(rdp);
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else
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WARN_ON_ONCE(rdp->cpu_no_qs.b.exp);
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}
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU.
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* Note that this does not necessarily mean that the task currently running
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* on the CPU is in a quiescent state: Instead, it means that the current
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* grace period need not wait on any RCU read-side critical section that
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* starts later on this CPU. It also means that if the current task is
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* in an RCU read-side critical section, it has already added itself to
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* some leaf rcu_node structure's ->blkd_tasks list. In addition to the
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* current task, there might be any number of other tasks blocked while
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* in an RCU read-side critical section.
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*
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* Unlike non-preemptible-RCU, quiescent state reports for expedited
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* grace periods are handled separately via deferred quiescent states
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* and context switch events.
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*
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* Callers to this function must disable preemption.
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*/
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static void rcu_qs(void)
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{
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RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
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if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) {
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trace_rcu_grace_period(TPS("rcu_preempt"),
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__this_cpu_read(rcu_data.gp_seq),
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TPS("cpuqs"));
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__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
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barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
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WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
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}
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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 interrupts.
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*/
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void rcu_note_context_switch(bool preempt)
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{
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struct task_struct *t = current;
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struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
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struct rcu_node *rnp;
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trace_rcu_utilization(TPS("Start context switch"));
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lockdep_assert_irqs_disabled();
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WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!");
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if (rcu_preempt_depth() > 0 &&
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!t->rcu_read_unlock_special.b.blocked) {
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/* Possibly blocking in an RCU read-side critical section. */
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rnp = rdp->mynode;
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raw_spin_lock_rcu_node(rnp);
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t->rcu_read_unlock_special.b.blocked = true;
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t->rcu_blocked_node = rnp;
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/*
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* Verify the CPU's sanity, trace the preemption, and
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* then queue the task as required based on the states
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* of any ongoing and expedited grace periods.
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*/
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WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp));
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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trace_rcu_preempt_task(rcu_state.name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gp_seq
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: rcu_seq_snap(&rnp->gp_seq));
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rcu_preempt_ctxt_queue(rnp, rdp);
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} else {
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rcu_preempt_deferred_qs(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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rcu_qs();
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if (rdp->cpu_no_qs.b.exp)
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rcu_report_exp_rdp(rdp);
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rcu_tasks_qs(current, preempt);
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trace_rcu_utilization(TPS("End context switch"));
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}
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EXPORT_SYMBOL_GPL(rcu_note_context_switch);
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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 READ_ONCE(rnp->gp_tasks) != NULL;
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}
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/* limit value for ->rcu_read_lock_nesting. */
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#define RCU_NEST_PMAX (INT_MAX / 2)
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static void rcu_preempt_read_enter(void)
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{
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WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1);
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}
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static int rcu_preempt_read_exit(void)
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{
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int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1;
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WRITE_ONCE(current->rcu_read_lock_nesting, ret);
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return ret;
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}
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static void rcu_preempt_depth_set(int val)
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{
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WRITE_ONCE(current->rcu_read_lock_nesting, val);
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}
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/*
|
|
* Preemptible RCU implementation for rcu_read_lock().
|
|
* Just increment ->rcu_read_lock_nesting, shared state will be updated
|
|
* if we block.
|
|
*/
|
|
void __rcu_read_lock(void)
|
|
{
|
|
rcu_preempt_read_enter();
|
|
if (IS_ENABLED(CONFIG_PROVE_LOCKING))
|
|
WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
|
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && rcu_state.gp_kthread)
|
|
WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, true);
|
|
barrier(); /* critical section after entry code. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_lock);
|
|
|
|
/*
|
|
* Preemptible RCU implementation for rcu_read_unlock().
|
|
* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
|
|
* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
|
|
* invoke rcu_read_unlock_special() to clean up after a context switch
|
|
* in an RCU read-side critical section and other special cases.
|
|
*/
|
|
void __rcu_read_unlock(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
barrier(); // critical section before exit code.
|
|
if (rcu_preempt_read_exit() == 0) {
|
|
barrier(); // critical-section exit before .s check.
|
|
if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
|
|
rcu_read_unlock_special(t);
|
|
}
|
|
if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
|
|
int rrln = rcu_preempt_depth();
|
|
|
|
WARN_ON_ONCE(rrln < 0 || rrln > RCU_NEST_PMAX);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(__rcu_read_unlock);
|
|
|
|
/*
|
|
* Advance a ->blkd_tasks-list pointer to the next entry, instead
|
|
* returning NULL if at the end of the list.
|
|
*/
|
|
static struct list_head *rcu_next_node_entry(struct task_struct *t,
|
|
struct rcu_node *rnp)
|
|
{
|
|
struct list_head *np;
|
|
|
|
np = t->rcu_node_entry.next;
|
|
if (np == &rnp->blkd_tasks)
|
|
np = NULL;
|
|
return np;
|
|
}
|
|
|
|
/*
|
|
* Return true if the specified rcu_node structure has tasks that were
|
|
* preempted within an RCU read-side critical section.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return !list_empty(&rnp->blkd_tasks);
|
|
}
|
|
|
|
/*
|
|
* Report deferred quiescent states. The deferral time can
|
|
* be quite short, for example, in the case of the call from
|
|
* rcu_read_unlock_special().
|
|
*/
|
|
static notrace void
|
|
rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
|
|
{
|
|
bool empty_exp;
|
|
bool empty_norm;
|
|
bool empty_exp_now;
|
|
struct list_head *np;
|
|
bool drop_boost_mutex = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
union rcu_special special;
|
|
|
|
/*
|
|
* If RCU core is waiting for this CPU to exit its critical section,
|
|
* report the fact that it has exited. Because irqs are disabled,
|
|
* t->rcu_read_unlock_special cannot change.
|
|
*/
|
|
special = t->rcu_read_unlock_special;
|
|
rdp = this_cpu_ptr(&rcu_data);
|
|
if (!special.s && !rdp->cpu_no_qs.b.exp) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
t->rcu_read_unlock_special.s = 0;
|
|
if (special.b.need_qs) {
|
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
|
|
rdp->cpu_no_qs.b.norm = false;
|
|
rcu_report_qs_rdp(rdp);
|
|
udelay(rcu_unlock_delay);
|
|
} else {
|
|
rcu_qs();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Respond to a request by an expedited grace period for a
|
|
* quiescent state from this CPU. Note that requests from
|
|
* tasks are handled when removing the task from the
|
|
* blocked-tasks list below.
|
|
*/
|
|
if (rdp->cpu_no_qs.b.exp)
|
|
rcu_report_exp_rdp(rdp);
|
|
|
|
/* Clean up if blocked during RCU read-side critical section. */
|
|
if (special.b.blocked) {
|
|
|
|
/*
|
|
* Remove this task from the list it blocked on. The task
|
|
* now remains queued on the rcu_node corresponding to the
|
|
* CPU it first blocked on, so there is no longer any need
|
|
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
|
|
*/
|
|
rnp = t->rcu_blocked_node;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
|
|
WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
|
|
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
|
|
WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
|
|
(!empty_norm || rnp->qsmask));
|
|
empty_exp = sync_rcu_exp_done(rnp);
|
|
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
|
|
np = rcu_next_node_entry(t, rnp);
|
|
list_del_init(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = NULL;
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
|
|
rnp->gp_seq, t->pid);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
WRITE_ONCE(rnp->gp_tasks, np);
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
WRITE_ONCE(rnp->exp_tasks, np);
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
|
|
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
|
|
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t;
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
WRITE_ONCE(rnp->boost_tasks, np);
|
|
}
|
|
|
|
/*
|
|
* If this was the last task on the current list, and if
|
|
* we aren't waiting on any CPUs, report the quiescent state.
|
|
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
|
|
* so we must take a snapshot of the expedited state.
|
|
*/
|
|
empty_exp_now = sync_rcu_exp_done(rnp);
|
|
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
|
|
rnp->gp_seq,
|
|
0, rnp->qsmask,
|
|
rnp->level,
|
|
rnp->grplo,
|
|
rnp->grphi,
|
|
!!rnp->gp_tasks);
|
|
rcu_report_unblock_qs_rnp(rnp, flags);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/*
|
|
* If this was the last task on the expedited lists,
|
|
* then we need to report up the rcu_node hierarchy.
|
|
*/
|
|
if (!empty_exp && empty_exp_now)
|
|
rcu_report_exp_rnp(rnp, true);
|
|
|
|
/* Unboost if we were boosted. */
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
|
|
rt_mutex_futex_unlock(&rnp->boost_mtx.rtmutex);
|
|
} else {
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Is a deferred quiescent-state pending, and are we also not in
|
|
* an RCU read-side critical section? It is the caller's responsibility
|
|
* to ensure it is otherwise safe to report any deferred quiescent
|
|
* states. The reason for this is that it is safe to report a
|
|
* quiescent state during context switch even though preemption
|
|
* is disabled. This function cannot be expected to understand these
|
|
* nuances, so the caller must handle them.
|
|
*/
|
|
static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
|
|
{
|
|
return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) ||
|
|
READ_ONCE(t->rcu_read_unlock_special.s)) &&
|
|
rcu_preempt_depth() == 0;
|
|
}
|
|
|
|
/*
|
|
* Report a deferred quiescent state if needed and safe to do so.
|
|
* As with rcu_preempt_need_deferred_qs(), "safe" involves only
|
|
* not being in an RCU read-side critical section. The caller must
|
|
* evaluate safety in terms of interrupt, softirq, and preemption
|
|
* disabling.
|
|
*/
|
|
notrace void rcu_preempt_deferred_qs(struct task_struct *t)
|
|
{
|
|
unsigned long flags;
|
|
|
|
if (!rcu_preempt_need_deferred_qs(t))
|
|
return;
|
|
local_irq_save(flags);
|
|
rcu_preempt_deferred_qs_irqrestore(t, flags);
|
|
}
|
|
|
|
/*
|
|
* Minimal handler to give the scheduler a chance to re-evaluate.
|
|
*/
|
|
static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
|
|
{
|
|
struct rcu_data *rdp;
|
|
|
|
rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
|
|
rdp->defer_qs_iw_pending = false;
|
|
}
|
|
|
|
/*
|
|
* Handle special cases during rcu_read_unlock(), such as needing to
|
|
* notify RCU core processing or task having blocked during the RCU
|
|
* read-side critical section.
|
|
*/
|
|
static void rcu_read_unlock_special(struct task_struct *t)
|
|
{
|
|
unsigned long flags;
|
|
bool irqs_were_disabled;
|
|
bool preempt_bh_were_disabled =
|
|
!!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
|
|
|
|
/* NMI handlers cannot block and cannot safely manipulate state. */
|
|
if (in_nmi())
|
|
return;
|
|
|
|
local_irq_save(flags);
|
|
irqs_were_disabled = irqs_disabled_flags(flags);
|
|
if (preempt_bh_were_disabled || irqs_were_disabled) {
|
|
bool expboost; // Expedited GP in flight or possible boosting.
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) ||
|
|
(rdp->grpmask & READ_ONCE(rnp->expmask)) ||
|
|
(IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
|
|
((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) ||
|
|
(IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled &&
|
|
t->rcu_blocked_node);
|
|
// Need to defer quiescent state until everything is enabled.
|
|
if (use_softirq && (in_hardirq() || (expboost && !irqs_were_disabled))) {
|
|
// Using softirq, safe to awaken, and either the
|
|
// wakeup is free or there is either an expedited
|
|
// GP in flight or a potential need to deboost.
|
|
raise_softirq_irqoff(RCU_SOFTIRQ);
|
|
} else {
|
|
// Enabling BH or preempt does reschedule, so...
|
|
// Also if no expediting and no possible deboosting,
|
|
// slow is OK. Plus nohz_full CPUs eventually get
|
|
// tick enabled.
|
|
set_tsk_need_resched(current);
|
|
set_preempt_need_resched();
|
|
if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
|
|
expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) {
|
|
// Get scheduler to re-evaluate and call hooks.
|
|
// If !IRQ_WORK, FQS scan will eventually IPI.
|
|
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) &&
|
|
IS_ENABLED(CONFIG_PREEMPT_RT))
|
|
rdp->defer_qs_iw = IRQ_WORK_INIT_HARD(
|
|
rcu_preempt_deferred_qs_handler);
|
|
else
|
|
init_irq_work(&rdp->defer_qs_iw,
|
|
rcu_preempt_deferred_qs_handler);
|
|
rdp->defer_qs_iw_pending = true;
|
|
irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
|
|
}
|
|
}
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
rcu_preempt_deferred_qs_irqrestore(t, flags);
|
|
}
|
|
|
|
/*
|
|
* 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 ->gp_seq.
|
|
*
|
|
* 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)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
|
|
dump_blkd_tasks(rnp, 10);
|
|
if (rcu_preempt_has_tasks(rnp) &&
|
|
(rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
|
|
WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
|
|
t = container_of(rnp->gp_tasks, struct task_struct,
|
|
rcu_node_entry);
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
|
|
rnp->gp_seq, t->pid);
|
|
}
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU, including voluntary
|
|
* context switches for Tasks RCU. When a task blocks, the task is
|
|
* recorded in the corresponding CPU's rcu_node structure, which is checked
|
|
* elsewhere, hence this function need only check for quiescent states
|
|
* related to the current CPU, not to those related to tasks.
|
|
*/
|
|
static void rcu_flavor_sched_clock_irq(int user)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_preempt_depth() > 0 ||
|
|
(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
|
|
/* No QS, force context switch if deferred. */
|
|
if (rcu_preempt_need_deferred_qs(t)) {
|
|
set_tsk_need_resched(t);
|
|
set_preempt_need_resched();
|
|
}
|
|
} else if (rcu_preempt_need_deferred_qs(t)) {
|
|
rcu_preempt_deferred_qs(t); /* Report deferred QS. */
|
|
return;
|
|
} else if (!WARN_ON_ONCE(rcu_preempt_depth())) {
|
|
rcu_qs(); /* Report immediate QS. */
|
|
return;
|
|
}
|
|
|
|
/* If GP is oldish, ask for help from rcu_read_unlock_special(). */
|
|
if (rcu_preempt_depth() > 0 &&
|
|
__this_cpu_read(rcu_data.core_needs_qs) &&
|
|
__this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
|
|
!t->rcu_read_unlock_special.b.need_qs &&
|
|
time_after(jiffies, rcu_state.gp_start + HZ))
|
|
t->rcu_read_unlock_special.b.need_qs = true;
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
* Besides, if this function does anything other than just immediately
|
|
* return, there was a bug of some sort. Spewing warnings from this
|
|
* function is like as not to simply obscure important prior warnings.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (unlikely(!list_empty(¤t->rcu_node_entry))) {
|
|
rcu_preempt_depth_set(1);
|
|
barrier();
|
|
WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
|
|
} else if (unlikely(rcu_preempt_depth())) {
|
|
rcu_preempt_depth_set(1);
|
|
} else {
|
|
return;
|
|
}
|
|
__rcu_read_unlock();
|
|
rcu_preempt_deferred_qs(current);
|
|
}
|
|
|
|
/*
|
|
* Dump the blocked-tasks state, but limit the list dump to the
|
|
* specified number of elements.
|
|
*/
|
|
static void
|
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
|
{
|
|
int cpu;
|
|
int i;
|
|
struct list_head *lhp;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp1;
|
|
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
|
|
__func__, rnp->grplo, rnp->grphi, rnp->level,
|
|
(long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs);
|
|
for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
|
|
pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
|
|
__func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
|
|
pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
|
|
__func__, READ_ONCE(rnp->gp_tasks), data_race(rnp->boost_tasks),
|
|
READ_ONCE(rnp->exp_tasks));
|
|
pr_info("%s: ->blkd_tasks", __func__);
|
|
i = 0;
|
|
list_for_each(lhp, &rnp->blkd_tasks) {
|
|
pr_cont(" %p", lhp);
|
|
if (++i >= ncheck)
|
|
break;
|
|
}
|
|
pr_cont("\n");
|
|
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
|
|
rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
|
|
cpu, ".o"[rcu_rdp_cpu_online(rdp)],
|
|
(long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
|
|
(long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
|
|
}
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/*
|
|
* If strict grace periods are enabled, and if the calling
|
|
* __rcu_read_unlock() marks the beginning of a quiescent state, immediately
|
|
* report that quiescent state and, if requested, spin for a bit.
|
|
*/
|
|
void rcu_read_unlock_strict(void)
|
|
{
|
|
struct rcu_data *rdp;
|
|
|
|
if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread)
|
|
return;
|
|
rdp = this_cpu_ptr(&rcu_data);
|
|
rdp->cpu_no_qs.b.norm = false;
|
|
rcu_report_qs_rdp(rdp);
|
|
udelay(rcu_unlock_delay);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_read_unlock_strict);
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
pr_info("Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Note a quiescent state for PREEMPTION=n. Because we do not need to know
|
|
* how many quiescent states passed, just if there was at least one since
|
|
* the start of the grace period, this just sets a flag. The caller must
|
|
* have disabled preemption.
|
|
*/
|
|
static void rcu_qs(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
|
|
if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
|
|
return;
|
|
trace_rcu_grace_period(TPS("rcu_sched"),
|
|
__this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
|
|
__this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
|
|
if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
|
|
rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
|
|
}
|
|
|
|
/*
|
|
* Register an urgently needed quiescent state. If there is an
|
|
* emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
|
|
* dyntick-idle quiescent state visible to other CPUs, which will in
|
|
* some cases serve for expedited as well as normal grace periods.
|
|
* Either way, register a lightweight quiescent state.
|
|
*/
|
|
void rcu_all_qs(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
|
|
return;
|
|
preempt_disable(); // For CONFIG_PREEMPT_COUNT=y kernels
|
|
/* Load rcu_urgent_qs before other flags. */
|
|
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
|
|
preempt_enable();
|
|
return;
|
|
}
|
|
this_cpu_write(rcu_data.rcu_urgent_qs, false);
|
|
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
|
|
local_irq_save(flags);
|
|
rcu_momentary_dyntick_idle();
|
|
local_irq_restore(flags);
|
|
}
|
|
rcu_qs();
|
|
preempt_enable();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_all_qs);
|
|
|
|
/*
|
|
* Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
|
|
*/
|
|
void rcu_note_context_switch(bool preempt)
|
|
{
|
|
trace_rcu_utilization(TPS("Start context switch"));
|
|
rcu_qs();
|
|
/* Load rcu_urgent_qs before other flags. */
|
|
if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
|
|
goto out;
|
|
this_cpu_write(rcu_data.rcu_urgent_qs, false);
|
|
if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
|
|
rcu_momentary_dyntick_idle();
|
|
out:
|
|
rcu_tasks_qs(current, preempt);
|
|
trace_rcu_utilization(TPS("End context switch"));
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_note_context_switch);
|
|
|
|
/*
|
|
* 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;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no deferred quiescent
|
|
* states.
|
|
*/
|
|
static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
// Except that we do need to respond to a request by an expedited
|
|
// grace period for a quiescent state from this CPU. Note that in
|
|
// non-preemptible kernels, there can be no context switches within RCU
|
|
// read-side critical sections, which in turn means that the leaf rcu_node
|
|
// structure's blocked-tasks list is always empty. is therefore no need to
|
|
// actually check it. Instead, a quiescent state from this CPU suffices,
|
|
// and this function is only called from such a quiescent state.
|
|
notrace void rcu_preempt_deferred_qs(struct task_struct *t)
|
|
{
|
|
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
|
|
|
|
if (rdp->cpu_no_qs.b.exp)
|
|
rcu_report_exp_rdp(rdp);
|
|
}
|
|
|
|
/*
|
|
* 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);
|
|
}
|
|
|
|
/*
|
|
* Check to see if this CPU is in a non-context-switch quiescent state,
|
|
* namely user mode and idle loop.
|
|
*/
|
|
static void rcu_flavor_sched_clock_irq(int user)
|
|
{
|
|
if (user || rcu_is_cpu_rrupt_from_idle()) {
|
|
|
|
/*
|
|
* Get here if this CPU took its interrupt from user
|
|
* mode or from the idle loop, and if this is not a
|
|
* nested interrupt. In this case, the CPU is in
|
|
* a quiescent state, so note it.
|
|
*
|
|
* No memory barrier is required here because rcu_qs()
|
|
* references only CPU-local variables that other CPUs
|
|
* neither access nor modify, at least not while the
|
|
* corresponding CPU is online.
|
|
*/
|
|
rcu_qs();
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
|
* while in preemptible RCU read-side critical sections.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Dump the guaranteed-empty blocked-tasks state. Trust but verify.
|
|
*/
|
|
static void
|
|
dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
|
|
{
|
|
WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
/*
|
|
* If boosting, set rcuc kthreads to realtime priority.
|
|
*/
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
|
|
#ifdef CONFIG_RCU_BOOST
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
WRITE_ONCE(rdp->rcuc_activity, jiffies);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp)
|
|
{
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
return rdp->nocb_cb_kthread == current;
|
|
#else
|
|
return false;
|
|
#endif
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(struct rcu_data *rdp)
|
|
{
|
|
return rdp->rcu_cpu_kthread_task == current ||
|
|
rcu_is_callbacks_nocb_kthread(rdp);
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
/*
|
|
* 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 task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (READ_ONCE(rnp->exp_tasks) == NULL &&
|
|
READ_ONCE(rnp->boost_tasks) == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, 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_rcu_node(rnp, 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;
|
|
else
|
|
tb = rnp->boost_tasks;
|
|
|
|
/*
|
|
* 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(&rnp->boost_mtx.rtmutex, t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
/* Lock only for side effect: boosts task t's priority. */
|
|
rt_mutex_lock(&rnp->boost_mtx);
|
|
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
|
|
rnp->n_boosts++;
|
|
|
|
return READ_ONCE(rnp->exp_tasks) != NULL ||
|
|
READ_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread, one per leaf 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 (;;) {
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_WAITING);
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
|
rcu_wait(READ_ONCE(rnp->boost_tasks) ||
|
|
READ_ONCE(rnp->exp_tasks));
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_RUNNING);
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
WRITE_ONCE(rnp->boost_kthread_status, RCU_KTHREAD_YIELDING);
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
|
schedule_timeout_idle(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)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_lockdep_assert_held_rcu_node(rnp);
|
|
if (!rnp->boost_kthread_task ||
|
|
(!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
(!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld ||
|
|
IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
rcu_wake_cond(rnp->boost_kthread_task,
|
|
READ_ONCE(rnp->boost_kthread_status));
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
}
|
|
|
|
#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.
|
|
*/
|
|
static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
int rnp_index = rnp - rcu_get_root();
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
mutex_lock(&rnp->boost_kthread_mutex);
|
|
if (rnp->boost_kthread_task || !rcu_scheduler_fully_active)
|
|
goto out;
|
|
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (WARN_ON_ONCE(IS_ERR(t)))
|
|
goto out;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
|
|
out:
|
|
mutex_unlock(&rnp->boost_kthread_mutex);
|
|
}
|
|
|
|
/*
|
|
* 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.
|
|
*
|
|
* Any future concurrent calls are serialized via ->boost_kthread_mutex.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask;
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
mutex_lock(&rnp->boost_kthread_mutex);
|
|
mask = rcu_rnp_online_cpus(rnp);
|
|
for_each_leaf_node_possible_cpu(rnp, cpu)
|
|
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
|
cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
|
|
if (cpumask_empty(cm)) {
|
|
cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
|
|
if (outgoingcpu >= 0)
|
|
cpumask_clear_cpu(outgoingcpu, cm);
|
|
}
|
|
set_cpus_allowed_ptr(t, cm);
|
|
mutex_unlock(&rnp->boost_kthread_mutex);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/*
|
|
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
|
|
* grace-period kthread will do force_quiescent_state() processing?
|
|
* The idea is to avoid waking up RCU core processing on such a
|
|
* CPU unless the grace period has extended for too long.
|
|
*
|
|
* This code relies on the fact that all NO_HZ_FULL CPUs are also
|
|
* RCU_NOCB_CPU CPUs.
|
|
*/
|
|
static bool rcu_nohz_full_cpu(void)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(smp_processor_id()) &&
|
|
(!rcu_gp_in_progress() ||
|
|
time_before(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
|
|
return true;
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Bind the RCU grace-period kthreads to the housekeeping CPU.
|
|
*/
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
if (!tick_nohz_full_enabled())
|
|
return;
|
|
housekeeping_affine(current, HK_TYPE_RCU);
|
|
}
|