The "thread would block" case can be checked without grabbing the lock
Signed-off-by: Nicholas Mc Guire <der.h...@hofr.at>
---
v2: return type is boot thus return should be false not 0 here
Reported-by kbuild test robot <fengguang...@intel.com>
If the check does not return early then grab the lock and recheck.
A memory barrier is not needed as complete() and complete_all() imply
a barrier.
The ACCESS_ONCE is needed for calls in a loop that, if inlined, could
optimize out the re-fetching of x->done.
kernel/sched/completion.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 7c5cd70..5f7cf31 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -268,6 +268,15 @@ bool try_wait_for_completion(struct completion *x)
unsigned long flags;
int ret = 1;
+ /*
+ * Since x->done will need to be locked only
+ * in the non-blocking case, we check x->done
+ * first without taking the lock so we can
+ * return early in the blocking case.
+ */
+ if (!ACCESS_ONCE(x->done))
+ return false;
+
spin_lock_irqsave(&x->wait.lock, flags);
if (!x->done)
ret = 0;
--
1.7.10.4
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