Commit-ID: 38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd Gitweb: http://git.kernel.org/tip/38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd Author: Darren Hart (VMware) <dvh...@infradead.org> AuthorDate: Fri, 14 Apr 2017 15:31:38 -0700 Committer: Thomas Gleixner <t...@linutronix.de> CommitDate: Sat, 15 Apr 2017 16:03:46 +0200
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) <dvh...@infradead.org> Cc: Peter Zijlstra <pet...@infradead.org> Link: http://lkml.kernel.org/r/20170414223138.GA4222@fury Signed-off-by: Thomas Gleixner <t...@linutronix.de> --- 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); }
