Commit-ID: 7a6b55e7108b3476d13ee9501ec69dbe1605d774
Gitweb: http://git.kernel.org/tip/7a6b55e7108b3476d13ee9501ec69dbe1605d774
Author: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
AuthorDate: Thu, 29 Nov 2012 16:46:09 +0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 7 Feb 2013 15:19:36 -0800
srcu: use ACCESS_ONCE() to access sp->completed in srcu_read_lock()
The old SRCU implementation loads sp->completed within an
RCU-sched section, courtesy of preempt_disable(). This was required
due to the use of synchronize_sched() in the old implemenation's
synchronize_srcu(). However, the new implementation does not rely
on synchronize_sched(), so it in turn does not require the load of
sp->completed and the ->c[] counter to be in a single preempt-disabled
region of code. This commit therefore moves the sp->completed access
outside of the preempt-disabled region and applies ACCESS_ONCE().
The resulting code is almost as the same as before, but it removes the
now-misleading rcu_dereference_index_check() call.
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/srcu.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/kernel/srcu.c b/kernel/srcu.c
index e34f299..01d5ccb 100644
--- a/kernel/srcu.c
+++ b/kernel/srcu.c
@@ -298,9 +298,8 @@ int __srcu_read_lock(struct srcu_struct *sp)
{
int idx;
+ idx = ACCESS_ONCE(sp->completed) & 0x1;
preempt_disable();
- idx = rcu_dereference_index_check(sp->completed,
- rcu_read_lock_sched_held()) & 0x1;
ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
smp_mb(); /* B */ /* Avoid leaking the critical section. */
ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
--
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