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rcu: Make exit_rcu() more precise and consolidate

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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
This commit is contained in:
Paul E. McKenney
2012-04-13 12:54:22 -07:00
committed by Paul E. McKenney
parent 616c310e83
commit 9dd8fb16c3
6 changed files with 29 additions and 49 deletions
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16
kernel/rcutiny_plugin.h
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@@ -851,22 +851,6 @@ int rcu_preempt_needs_cpu(void)
return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
}
/*
* Check for a task exiting while in a preemptible -RCU read-side
* critical section, clean up if so. No need to issue warnings,
* as debug_check_no_locks_held() already does this if lockdep
* is enabled.
*/
void exit_rcu(void)
{
struct task_struct *t = current;
if (t->rcu_read_lock_nesting == 0)
return;
t->rcu_read_lock_nesting = 1;
__rcu_read_unlock();
}
#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
#ifdef CONFIG_RCU_TRACE