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authorDarren Hart (VMware) <dvhart@infradead.org>2017-04-14 15:31:38 -0700
committerThomas Gleixner <tglx@linutronix.de>2017-04-15 16:03:46 +0200
commit38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd (patch)
treea5b9dd2ff5d7ba22e0953270de1b63290e29df03 /kernel/futex.c
parent94ffac5d847cfd790bb37b7cef1cad803743985e (diff)
futex: Clarify mark_wake_futex memory barrier usage
Clarify the scenario described in mark_wake_futex requiring the smp_store_release(). Update the comment to explicitly refer to the plist_del now under __unqueue_futex() (previously plist_del was in the same function as the comment). Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20170414223138.GA4222@fury Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c9
1 files changed, 5 insertions, 4 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index ede2f1ef8511..357348a6cf6b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1380,10 +1380,11 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
wake_q_add(wake_q, p);
__unqueue_futex(q);
/*
- * The waiting task can free the futex_q as soon as
- * q->lock_ptr = NULL is written, without taking any locks. A
- * memory barrier is required here to prevent the following
- * store to lock_ptr from getting ahead of the plist_del.
+ * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
+ * is written, without taking any locks. This is possible in the event
+ * of a spurious wakeup, for example. A memory barrier is required here
+ * to prevent the following store to lock_ptr from getting ahead of the
+ * plist_del in __unqueue_futex().
*/
smp_store_release(&q->lock_ptr, NULL);
}