[PATCH -v4 04/10] futex: Use smp_store_release() in mark_wake_futex()

From: Peter Zijlstra
Date: Tue Dec 13 2016 - 04:02:44 EST


Since the futex_q can dissapear the instruction after assigning NULL,
this really should be a RELEASE barrier. That stops loads from hitting
dead memory too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/futex.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1288,8 +1288,7 @@ static void mark_wake_futex(struct wake_
* memory barrier is required here to prevent the following
* store to lock_ptr from getting ahead of the plist_del.
*/
- smp_wmb();
- q->lock_ptr = NULL;
+ smp_store_release(&q->lock_ptr, NULL);
}

static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter,