Messages in this thread Patch in this message | | | Subject | [PATCH v2 3/3] sched: Avoid that abort_exclusive_wait() triggers spurious wakeups | From | Bart Van Assche <> | Date | Fri, 5 Aug 2016 16:10:18 -0700 |
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Patch "sched: Avoid that __wait_on_bit_lock() hangs" made spurious wakeups possible. Avoid to trigger such spurious wakeups.
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Neil Brown <neilb@suse.de> Cc: Michael Shaver <jmshaver@gmail.com> --- include/linux/wait.h | 5 +++-- kernel/sched/wait.c | 21 ++++++++------------- 2 files changed, 11 insertions(+), 15 deletions(-)
diff --git a/include/linux/wait.h b/include/linux/wait.h index 27d7a0a..5034fce 100644 --- a/include/linux/wait.h +++ b/include/linux/wait.h @@ -282,7 +282,7 @@ wait_queue_head_t *bit_waitqueue(void *, int); __ret = __int; \ if (exclusive) { \ abort_exclusive_wait(&wq, &__wait, \ - state, NULL); \ + condition, state, NULL); \ goto __out; \ } \ break; \ @@ -976,7 +976,8 @@ void prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state); void prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state); long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state); void finish_wait(wait_queue_head_t *q, wait_queue_t *wait); -void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, unsigned int mode, void *key); +void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, + bool wake_up_next, unsigned int mode, void *key); long wait_woken(wait_queue_t *wait, unsigned mode, long timeout); int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key); int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key); diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c index dcc7693..c5a913f 100644 --- a/kernel/sched/wait.c +++ b/kernel/sched/wait.c @@ -259,6 +259,7 @@ EXPORT_SYMBOL(finish_wait); * abort_exclusive_wait - abort exclusive waiting in a queue * @q: waitqueue waited on * @wait: wait descriptor + * @wake_up_next: Whether or not to wake up another exclusive waiter * @mode: runstate of the waiter to be woken * @key: key to identify a wait bit queue or %NULL * @@ -266,19 +267,12 @@ EXPORT_SYMBOL(finish_wait); * the wait descriptor from the given waitqueue if still * queued. * - * Wakes up the next waiter to prevent waiter starvation - * when an exclusive waiter aborts and is woken up - * concurrently and no one wakes up the next waiter. Note: - * even when a signal is pending it is possible that - * __wake_up_common() wakes up the current thread and hence - * that @wait has been removed from the wait queue @q. Hence - * test whether there are more waiters on the wait queue - * even if @wait is not on the wait queue @q. This approach - * will cause a spurious wakeup if a signal is delivered and - * no other thread calls __wake_up_common() concurrently. + * Wakes up the next waiter if @wake_up_next is set to prevent + * waiter starvation when an exclusive waiter aborts and is + * woken up concurrently and no one wakes up the next waiter. */ void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, - unsigned int mode, void *key) + bool wake_up_next, unsigned int mode, void *key) { unsigned long flags; @@ -286,7 +280,7 @@ void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, spin_lock_irqsave(&q->lock, flags); if (!list_empty(&wait->task_list)) list_del_init(&wait->task_list); - if (waitqueue_active(q)) + if (wake_up_next && waitqueue_active(q)) __wake_up_locked_key(q, mode, key); spin_unlock_irqrestore(&q->lock, flags); } @@ -440,7 +434,8 @@ __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q, ret = action(key, mode); if (!ret) continue; - abort_exclusive_wait(wq, &q->wait, mode, key); + abort_exclusive_wait(wq, &q->wait, + test_bit(key->bit_nr, key->flags), mode, key); return ret; } while (test_and_set_bit(key->bit_nr, key->flags)); finish_wait(wq, &q->wait); -- 2.9.2
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