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.vanass...@sandisk.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Johannes Weiner <han...@cmpxchg.org>
Cc: Neil Brown <ne...@suse.de>
Cc: Michael Shaver <jmsha...@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
