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Date: Fri, 14 Apr 2017 15:31:38 -0700 From: "Darren Hart (VMware)" <dvhart@...radead.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org> Subject: [PATCH] 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@...radead.org> Cc: Thomas Gleixner <tglx@...utronix.de> Cc: Ingo Molnar <mingo@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org> --- kernel/futex.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/kernel/futex.c b/kernel/futex.c index ede2f1e..357348a 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); } -- 2.9.3 -- Darren Hart VMware Open Source Technology Center
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