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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@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Paul E. McKenney 2017-06-29 12:47:04 -07:00
parent 23a9b748a3
commit dec13c42d2
1 changed files with 4 additions and 7 deletions
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11
kernel/sched/completion.c
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@ -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);