futex: Clarify mark_wake_futex memory barrier usage
PATCH 1/1 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) <[email protected]>
Cc Thomas Gleixner <[email protected]>
Cc Ingo Molnar <[email protected]>
Cc Peter Zijlstra <[email protected]>
--- kernel/futex.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
kernel/futex.c +5 -4
@@ -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 ); }
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merge botfutex: Clarify mark_wake_futex memory barrier usage
Commit-ID: 38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd Gitweb: http://git.kernel.org/tip/38fcd06e9b7f6855db1f3ebac5e18b8fdb467ffd Author: Darren Hart (VMware) <[email protected]> AuthorDate: Fri, 14 Apr 2017 15:31:38 -0700 Committer: Thomas Gleixner <[email protected]> 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) <[email protected]>
Cc Peter Zijlstra <[email protected]>
Signed-off-by Thomas Gleixner <[email protected]>
--- kernel/futex.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)
kernel/futex.c +5 -4
@@ -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 ); }