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rcu: Remove fast check path from __synchronize_srcu()

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The fastpath in __synchronize_srcu() is designed to handle cases where
there are a large number of concurrent calls for the same srcu_struct
structure.  However, the Linux kernel currently does not use SRCU in
this manner, so remove the fastpath checks for simplicity.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Lai Jiangshan 2012-02-22 13:06:51 -08:00 committed by Paul E. McKenney
parent cef50120b6
commit 4b7a3e9e32
1 changed files with 1 additions and 24 deletions
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25
kernel/srcu.c
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@ -308,7 +308,7 @@ static void flip_idx_and_wait(struct srcu_struct *sp, bool expedited)
*/ */
static void __synchronize_srcu(struct srcu_struct *sp, bool expedited) static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
{ {
int idx; int idx = 0;
rcu_lockdep_assert(!lock_is_held(&sp->dep_map) && rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
!lock_is_held(&rcu_bh_lock_map) && !lock_is_held(&rcu_bh_lock_map) &&
@ -316,31 +316,8 @@ static void __synchronize_srcu(struct srcu_struct *sp, bool expedited)
!lock_is_held(&rcu_sched_lock_map), !lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section"); "Illegal synchronize_srcu() in same-type SRCU (or RCU) read-side critical section");
smp_mb(); /* Ensure prior action happens before grace period. */
idx = ACCESS_ONCE(sp->completed);
smp_mb(); /* Access to ->completed before lock acquisition. */
mutex_lock(&sp->mutex); mutex_lock(&sp->mutex);
/*
* Check to see if someone else did the work for us while we were
* waiting to acquire the lock. We need -three- advances of
* the counter, not just one. If there was but one, we might have
* shown up -after- our helper's first synchronize_sched(), thus
* having failed to prevent CPU-reordering races with concurrent
* srcu_read_unlock()s on other CPUs (see comment below). If there
* was only two, we are guaranteed to have waited through only one
* full index-flip phase. So we either (1) wait for three or
* (2) supply the additional ones we need.
*/
if (sp->completed == idx + 2)
idx = 1;
else if (sp->completed == idx + 3) {
mutex_unlock(&sp->mutex);
return;
} else
idx = 0;
/* /*
* If there were no helpers, then we need to do two flips of * If there were no helpers, then we need to do two flips of
* the index. The first flip is required if there are any * the index. The first flip is required if there are any