Commit-ID: dec13c42d21a96adc5d0d25510d0b59775dfd2ec
Gitweb: http://git.kernel.org/tip/dec13c42d21a96adc5d0d25510d0b59775dfd2ec
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Thu, 29 Jun 2017 12:47:04 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 17 Aug 2017 08:06:44 -0700
completion: Replace spin_unlock_wait() with lock/unlock pair
There is no agreed-upon definition of spin_unlock_wait()'s semantics,
and it appears that all callers could do just as well with a lock/unlock
pair. This commit therefore replaces the spin_unlock_wait() call in
completion_done() with spin_lock() followed immediately by spin_unlock().
This should be safe from a performance perspective because the lock
will be held only the wakeup happens really quickly.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Cc: Andrea Parri <parri.andrea@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
kernel/sched/completion.c | 11 ++++-------
1 file changed, 4 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 13fc5ae..c9524d2 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -300,6 +300,8 @@ EXPORT_SYMBOL(try_wait_for_completion);
*/
bool completion_done(struct completion *x)
{
+ unsigned long flags;
+
if (!READ_ONCE(x->done))
return false;
@@ -307,14 +309,9 @@ bool completion_done(struct completion *x)
* If ->done, we need to wait for complete() to release ->wait.lock
* otherwise we can end up freeing the completion before complete()
* is done referencing it.
- *
- * The RMB pairs with complete()'s RELEASE of ->wait.lock and orders
- * the loads of ->done and ->wait.lock such that we cannot observe
- * the lock before complete() acquires it while observing the ->done
- * after it's acquired the lock.
*/
- smp_rmb();
- spin_unlock_wait(&x->wait.lock);
+ spin_lock_irqsave(&x->wait.lock, flags);
+ spin_unlock_irqrestore(&x->wait.lock, flags);
return true;
}
EXPORT_SYMBOL(completion_done);
--
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