From 7a6b55e7108b3476d13ee9501ec69dbe1605d774 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Thu, 29 Nov 2012 16:46:09 +0800 Subject: [PATCH] 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 Signed-off-by: Paul E. McKenney --- kernel/srcu.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/srcu.c b/kernel/srcu.c index e34f2991ed41..01d5ccb8bfe3 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;