linux-kernel - [PATCH 1/2] sched/wait: abort_exclusive_wait() should pass TASK_NORMAL to wake

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Message-ID: <20160826124528.GA28904@redhat.com>
Date:   Fri, 26 Aug 2016 14:45:28 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Bart Van Assche <bvanassche@....org>,
        Johannes Weiner <hannes@...xchg.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Neil Brown <neilb@...e.de>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] sched/wait: abort_exclusive_wait() should pass
 TASK_NORMAL to wake_up()

Otherwise this logic only works if mode is "compatible" with another
exclusive waiter.

If some wq has both TASK_INTERRUPTIBLE and TASK_UNINTERRUPTIBLE waiters,
abort_exclusive_wait() won't wait an uninterruptible waiter.

The main user is __wait_on_bit_lock() and currently it is fine but only
because TASK_KILLABLE includes TASK_UNINTERRUPTIBLE and we do not have
lock_page_interruptible() yet.

Just use TASK_NORMAL and remove the "mode" arg from abort_exclusive_wait().
Yes, this means that (say) wake_up_interruptible() can wake up the non-
interruptible waiter(s), but I think this is fine. And in fact I think
that abort_exclusive_wait() must die, see the next change.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 include/linux/wait.h | 6 +++---
 kernel/sched/wait.c  | 8 +++-----
 2 files changed, 6 insertions(+), 8 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 27d7a0a..329f796 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -281,8 +281,8 @@ wait_queue_head_t *bit_waitqueue(void *, int);
 		if (___wait_is_interruptible(state) && __int) {		\
 			__ret = __int;					\
 			if (exclusive) {				\
-				abort_exclusive_wait(&wq, &__wait,	\
-						     state, NULL);	\
+				abort_exclusive_wait(&wq, &__wait, 	\
+						     NULL);		\
 				goto __out;				\
 			}						\
 			break;						\
@@ -976,7 +976,7 @@ 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, 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 f15d6b6..2bbba01 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -259,7 +259,6 @@ EXPORT_SYMBOL(finish_wait);
  * abort_exclusive_wait - abort exclusive waiting in a queue
  * @q: waitqueue waited on
  * @wait: wait descriptor
- * @mode: runstate of the waiter to be woken
  * @key: key to identify a wait bit queue or %NULL
  *
  * Sets current thread back to running state and removes
@@ -273,8 +272,7 @@ EXPORT_SYMBOL(finish_wait);
  * 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)
+void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, void *key)
 {
 	unsigned long flags;
 
@@ -283,7 +281,7 @@ void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
 	if (!list_empty(&wait->task_list))
 		list_del_init(&wait->task_list);
 	else if (waitqueue_active(q))
-		__wake_up_locked_key(q, mode, key);
+		__wake_up_locked_key(q, TASK_NORMAL, key);
 	spin_unlock_irqrestore(&q->lock, flags);
 }
 EXPORT_SYMBOL(abort_exclusive_wait);
@@ -434,7 +432,7 @@ __wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
 		ret = action(&q->key, mode);
 		if (!ret)
 			continue;
-		abort_exclusive_wait(wq, &q->wait, mode, &q->key);
+		abort_exclusive_wait(wq, &q->wait, &q->key);
 		return ret;
 	} while (test_and_set_bit(q->key.bit_nr, q->key.flags));
 	finish_wait(wq, &q->wait);
-- 
2.5.0