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![Paul E. McKenney](/assets/img/avatar_default.png)
When running preemptible RCU, if a task exits in an RCU read-side critical section having blocked within that same RCU read-side critical section, the task must be removed from the list of tasks blocking a grace period (perhaps the current grace period, perhaps the next grace period, depending on timing). The exit() path invokes exit_rcu() to do this cleanup. However, the current implementation of exit_rcu() needlessly does the cleanup even if the task did not block within the current RCU read-side critical section, which wastes time and needlessly increases the size of the state space. Fix this by only doing the cleanup if the current task is actually on the list of tasks blocking some grace period. While we are at it, consolidate the two identical exit_rcu() functions into a single function. Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Tested-by: Linus Torvalds <torvalds@linux-foundation.org> Conflicts: kernel/rcupdate.c
363 lines
10 KiB
C
363 lines
10 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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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 IBM Corporation, 2001
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*
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* Authors: Dipankar Sarma <dipankar@in.ibm.com>
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* Manfred Spraul <manfred@colorfullife.com>
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <linux/atomic.h>
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#include <linux/bitops.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/cpu.h>
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#include <linux/mutex.h>
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#include <linux/export.h>
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#include <linux/hardirq.h>
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#define CREATE_TRACE_POINTS
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#include <trace/events/rcu.h>
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#include "rcu.h"
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#ifdef CONFIG_PREEMPT_RCU
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/*
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* Check for a task exiting while in a preemptible-RCU read-side
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* critical section, clean up if so. No need to issue warnings,
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* as debug_check_no_locks_held() already does this if lockdep
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* is enabled.
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*/
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void exit_rcu(void)
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{
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struct task_struct *t = current;
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if (likely(list_empty(¤t->rcu_node_entry)))
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return;
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t->rcu_read_lock_nesting = 1;
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barrier();
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t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
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__rcu_read_unlock();
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}
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#else /* #ifdef CONFIG_PREEMPT_RCU */
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void exit_rcu(void)
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{
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static struct lock_class_key rcu_lock_key;
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struct lockdep_map rcu_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
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EXPORT_SYMBOL_GPL(rcu_lock_map);
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static struct lock_class_key rcu_bh_lock_key;
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struct lockdep_map rcu_bh_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
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EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
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static struct lock_class_key rcu_sched_lock_key;
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struct lockdep_map rcu_sched_lock_map =
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STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
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EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
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#endif
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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int debug_lockdep_rcu_enabled(void)
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{
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return rcu_scheduler_active && debug_locks &&
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current->lockdep_recursion == 0;
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}
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EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
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/**
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* rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
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*
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* Check for bottom half being disabled, which covers both the
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* CONFIG_PROVE_RCU and not cases. Note that if someone uses
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* rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
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* will show the situation. This is useful for debug checks in functions
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* that require that they be called within an RCU read-side critical
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* section.
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*
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* Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
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*
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* Note that rcu_read_lock() is disallowed if the CPU is either idle or
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* offline from an RCU perspective, so check for those as well.
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*/
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int rcu_read_lock_bh_held(void)
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{
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (rcu_is_cpu_idle())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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return in_softirq() || irqs_disabled();
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}
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EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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struct rcu_synchronize {
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struct rcu_head head;
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struct completion completion;
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};
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/*
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* Awaken the corresponding synchronize_rcu() instance now that a
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* grace period has elapsed.
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*/
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static void wakeme_after_rcu(struct rcu_head *head)
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{
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struct rcu_synchronize *rcu;
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rcu = container_of(head, struct rcu_synchronize, head);
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complete(&rcu->completion);
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}
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void wait_rcu_gp(call_rcu_func_t crf)
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{
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struct rcu_synchronize rcu;
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init_rcu_head_on_stack(&rcu.head);
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init_completion(&rcu.completion);
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/* Will wake me after RCU finished. */
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crf(&rcu.head, wakeme_after_rcu);
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/* Wait for it. */
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wait_for_completion(&rcu.completion);
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destroy_rcu_head_on_stack(&rcu.head);
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}
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EXPORT_SYMBOL_GPL(wait_rcu_gp);
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#ifdef CONFIG_PROVE_RCU
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/*
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* wrapper function to avoid #include problems.
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*/
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int rcu_my_thread_group_empty(void)
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{
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return thread_group_empty(current);
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}
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EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
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#endif /* #ifdef CONFIG_PROVE_RCU */
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#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
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static inline void debug_init_rcu_head(struct rcu_head *head)
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{
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debug_object_init(head, &rcuhead_debug_descr);
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}
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static inline void debug_rcu_head_free(struct rcu_head *head)
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{
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debug_object_free(head, &rcuhead_debug_descr);
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}
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/*
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* fixup_init is called when:
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* - an active object is initialized
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*/
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static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
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{
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struct rcu_head *head = addr;
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switch (state) {
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case ODEBUG_STATE_ACTIVE:
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/*
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* Ensure that queued callbacks are all executed.
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* If we detect that we are nested in a RCU read-side critical
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* section, we should simply fail, otherwise we would deadlock.
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* In !PREEMPT configurations, there is no way to tell if we are
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* in a RCU read-side critical section or not, so we never
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* attempt any fixup and just print a warning.
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*/
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#ifndef CONFIG_PREEMPT
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WARN_ON_ONCE(1);
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return 0;
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#endif
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if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
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irqs_disabled()) {
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WARN_ON_ONCE(1);
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return 0;
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}
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rcu_barrier();
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rcu_barrier_sched();
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rcu_barrier_bh();
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debug_object_init(head, &rcuhead_debug_descr);
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return 1;
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default:
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return 0;
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}
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}
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/*
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* fixup_activate is called when:
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* - an active object is activated
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* - an unknown object is activated (might be a statically initialized object)
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* Activation is performed internally by call_rcu().
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*/
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static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
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{
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struct rcu_head *head = addr;
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switch (state) {
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case ODEBUG_STATE_NOTAVAILABLE:
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/*
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* This is not really a fixup. We just make sure that it is
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* tracked in the object tracker.
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*/
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debug_object_init(head, &rcuhead_debug_descr);
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debug_object_activate(head, &rcuhead_debug_descr);
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return 0;
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case ODEBUG_STATE_ACTIVE:
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/*
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* Ensure that queued callbacks are all executed.
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* If we detect that we are nested in a RCU read-side critical
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* section, we should simply fail, otherwise we would deadlock.
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* In !PREEMPT configurations, there is no way to tell if we are
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* in a RCU read-side critical section or not, so we never
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* attempt any fixup and just print a warning.
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*/
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#ifndef CONFIG_PREEMPT
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WARN_ON_ONCE(1);
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return 0;
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#endif
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if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
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irqs_disabled()) {
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WARN_ON_ONCE(1);
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return 0;
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}
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rcu_barrier();
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rcu_barrier_sched();
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rcu_barrier_bh();
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debug_object_activate(head, &rcuhead_debug_descr);
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return 1;
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default:
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return 0;
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}
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}
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/*
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* fixup_free is called when:
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* - an active object is freed
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*/
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static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
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{
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struct rcu_head *head = addr;
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switch (state) {
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case ODEBUG_STATE_ACTIVE:
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/*
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* Ensure that queued callbacks are all executed.
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* If we detect that we are nested in a RCU read-side critical
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* section, we should simply fail, otherwise we would deadlock.
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* In !PREEMPT configurations, there is no way to tell if we are
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* in a RCU read-side critical section or not, so we never
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* attempt any fixup and just print a warning.
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*/
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#ifndef CONFIG_PREEMPT
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WARN_ON_ONCE(1);
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return 0;
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#endif
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if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
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irqs_disabled()) {
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WARN_ON_ONCE(1);
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return 0;
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}
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rcu_barrier();
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rcu_barrier_sched();
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rcu_barrier_bh();
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debug_object_free(head, &rcuhead_debug_descr);
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return 1;
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default:
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return 0;
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}
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}
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/**
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* init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
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* @head: pointer to rcu_head structure to be initialized
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*
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* This function informs debugobjects of a new rcu_head structure that
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* has been allocated as an auto variable on the stack. This function
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* is not required for rcu_head structures that are statically defined or
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* that are dynamically allocated on the heap. This function has no
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* effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
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*/
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void init_rcu_head_on_stack(struct rcu_head *head)
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{
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debug_object_init_on_stack(head, &rcuhead_debug_descr);
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}
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EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
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/**
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* destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
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* @head: pointer to rcu_head structure to be initialized
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*
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* This function informs debugobjects that an on-stack rcu_head structure
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* is about to go out of scope. As with init_rcu_head_on_stack(), this
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* function is not required for rcu_head structures that are statically
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* defined or that are dynamically allocated on the heap. Also as with
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* init_rcu_head_on_stack(), this function has no effect for
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* !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
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*/
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void destroy_rcu_head_on_stack(struct rcu_head *head)
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{
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debug_object_free(head, &rcuhead_debug_descr);
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}
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EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
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struct debug_obj_descr rcuhead_debug_descr = {
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.name = "rcu_head",
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.fixup_init = rcuhead_fixup_init,
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.fixup_activate = rcuhead_fixup_activate,
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.fixup_free = rcuhead_fixup_free,
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};
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EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
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#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
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void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
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{
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trace_rcu_torture_read(rcutorturename, rhp);
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}
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EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
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#else
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#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
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#endif
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