Merge branch 'linux-linaro-lsk-v4.4' into linux-linaro-lsk-v4.4-android

[firefly-linux-kernel-4.4.55.git] / kernel / sched / completion.c

diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 7052d3fd4e7bd87a29bd144cbca1086621040251..8d0f35debf35657689908a4b37df7230ba7d6710 100644 (file)
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -274,7 +274,7 @@ bool try_wait_for_completion(struct completion *x)
         * first without taking the lock so we can
         * return early in the blocking case.
         */
-       if (!ACCESS_ONCE(x->done))
+       if (!READ_ONCE(x->done))
                return 0;
 
        spin_lock_irqsave(&x->wait.lock, flags);
@@ -297,6 +297,21 @@ EXPORT_SYMBOL(try_wait_for_completion);
  */
 bool completion_done(struct completion *x)
 {
-       return !!ACCESS_ONCE(x->done);
+       if (!READ_ONCE(x->done))
+               return false;
+
+       /*
+        * 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);
+       return true;
 }
 EXPORT_SYMBOL(completion_done);