linux-kernel - [PATCH v2 3/3] sched: Avoid that abort_exclusive

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Message-ID: <f029d234-f700-f1d5-bdad-f20920178a9d@sandisk.com>
Date:	Fri, 5 Aug 2016 16:10:18 -0700
From:	Bart Van Assche <bart.vanassche@...disk.com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Neil Brown <neilb@...e.de>,
	Michael Shaver <jmshaver@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 3/3] sched: Avoid that abort_exclusive_wait() triggers
 spurious wakeups

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@...disk.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Neil Brown <neilb@...e.de>
Cc: Michael Shaver <jmshaver@...il.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