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author | Paul E. McKenney <paulmck@linux.ibm.com> | 2018-11-29 21:42:06 +0300 |
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committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-01-26 02:28:28 +0300 |
commit | e5bc3af7734f90278a47906d917852a85544510b (patch) | |
tree | 600c386d8d0605b7f7f16c3046042d0c66a2da00 /kernel/rcu/tree.c | |
parent | 3cd4ca47aa577689c2e6b295d8f52af0e6f26333 (diff) | |
download | linux-e5bc3af7734f90278a47906d917852a85544510b.tar.xz |
rcu: Consolidate PREEMPT and !PREEMPT synchronize_rcu()
Now that rcu_blocking_is_gp() makes the correct immediate-return
decision for both PREEMPT and !PREEMPT, a single implementation of
synchronize_rcu() will work correctly under both configurations.
This commit therefore eliminates a few lines of code by consolidating
the two implementations of synchronize_rcu().
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu/tree.c')
-rw-r--r-- | kernel/rcu/tree.c | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index fc37bec32731..e2bd42b2b563 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2950,6 +2950,79 @@ void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func) } EXPORT_SYMBOL_GPL(kfree_call_rcu); +/* + * During early boot, any blocking grace-period wait automatically + * implies a grace period. Later on, this is never the case for PREEMPT. + * + * Howevr, because a context switch is a grace period for !PREEMPT, any + * blocking grace-period wait automatically implies a grace period if + * there is only one CPU online at any point time during execution of + * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to + * occasionally incorrectly indicate that there are multiple CPUs online + * when there was in fact only one the whole time, as this just adds some + * overhead: RCU still operates correctly. + */ +static int rcu_blocking_is_gp(void) +{ + int ret; + + if (IS_ENABLED(CONFIG_PREEMPT)) + return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE; + might_sleep(); /* Check for RCU read-side critical section. */ + preempt_disable(); + ret = num_online_cpus() <= 1; + preempt_enable(); + return ret; +} + +/** + * synchronize_rcu - wait until a grace period has elapsed. + * + * Control will return to the caller some time after a full grace + * period has elapsed, in other words after all currently executing RCU + * read-side critical sections have completed. Note, however, that + * upon return from synchronize_rcu(), the caller might well be executing + * concurrently with new RCU read-side critical sections that began while + * synchronize_rcu() was waiting. RCU read-side critical sections are + * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. + * In addition, regions of code across which interrupts, preemption, or + * softirqs have been disabled also serve as RCU read-side critical + * sections. This includes hardware interrupt handlers, softirq handlers, + * and NMI handlers. + * + * Note that this guarantee implies further memory-ordering guarantees. + * On systems with more than one CPU, when synchronize_rcu() returns, + * each CPU is guaranteed to have executed a full memory barrier since + * the end of its last RCU read-side critical section whose beginning + * preceded the call to synchronize_rcu(). In addition, each CPU having + * an RCU read-side critical section that extends beyond the return from + * synchronize_rcu() is guaranteed to have executed a full memory barrier + * after the beginning of synchronize_rcu() and before the beginning of + * that RCU read-side critical section. Note that these guarantees include + * CPUs that are offline, idle, or executing in user mode, as well as CPUs + * that are executing in the kernel. + * + * Furthermore, if CPU A invoked synchronize_rcu(), which returned + * to its caller on CPU B, then both CPU A and CPU B are guaranteed + * to have executed a full memory barrier during the execution of + * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but + * again only if the system has more than one CPU). + */ +void synchronize_rcu(void) +{ + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_rcu() in RCU read-side critical section"); + if (rcu_blocking_is_gp()) + return; + if (rcu_gp_is_expedited()) + synchronize_rcu_expedited(); + else + wait_rcu_gp(call_rcu); +} +EXPORT_SYMBOL_GPL(synchronize_rcu); + /** * get_state_synchronize_rcu - Snapshot current RCU state * |