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| author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2012-11-29 08:46:09 (GMT) |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2013-02-07 23:19:36 (GMT) |
| commit | 7a6b55e7108b3476d13ee9501ec69dbe1605d774 (patch) | |
| tree | 9712b0a5f7c3b5d90f2625af369774cdb1334e6f /kernel/srcu.c | |
| parent | 49271ca60645d64197b28c0835fed39f74b1a2d7 (diff) | |
| download | linux-7a6b55e7108b3476d13ee9501ec69dbe1605d774.tar.xz | |
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@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel/srcu.c')
| -rw-r--r-- | kernel/srcu.c | 3 |
1 files changed, 1 insertions, 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; |