lkml.org 
[lkml]   [2016]   [Sep]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:sched/core] sched/wait: Avoid abort_exclusive_wait() in __wait_on_bit_lock()
Commit-ID:  eaf9ef52241b545fe63621266bfc6fd8b06559ff
Gitweb: http://git.kernel.org/tip/eaf9ef52241b545fe63621266bfc6fd8b06559ff
Author: Oleg Nesterov <oleg@redhat.com>
AuthorDate: Tue, 6 Sep 2016 16:00:53 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 30 Sep 2016 10:54:03 +0200

sched/wait: Avoid abort_exclusive_wait() in __wait_on_bit_lock()

__wait_on_bit_lock() doesn't need abort_exclusive_wait() too. Right
now it can't use prepare_to_wait_event() (see the next change), but
it can do the additional finish_wait() if action() fails.

abort_exclusive_wait() no longer has callers, remove it.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Bart Van Assche <bvanassche@acm.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Neil Brown <neilb@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20160906140053.GA6164@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/wait.h | 1 -
kernel/sched/wait.c | 64 +++++++++++++++++-----------------------------------
2 files changed, 21 insertions(+), 44 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 7261dcb..19c75f9 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -984,7 +984,6 @@ 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, 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 2612393..0cb615d 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -270,37 +270,6 @@ void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
}
EXPORT_SYMBOL(finish_wait);

-/**
- * abort_exclusive_wait - abort exclusive waiting in a queue
- * @q: waitqueue waited on
- * @wait: wait descriptor
- * @key: key to identify a wait bit queue or %NULL
- *
- * Sets current thread back to running state and removes
- * the wait descriptor from the given waitqueue if still
- * queued.
- *
- * Wakes up the next waiter if the caller is concurrently
- * woken up through the queue.
- *
- * This prevents waiter starvation where 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, void *key)
-{
- unsigned long flags;
-
- __set_current_state(TASK_RUNNING);
- spin_lock_irqsave(&q->lock, flags);
- if (!list_empty(&wait->task_list))
- list_del_init(&wait->task_list);
- else if (waitqueue_active(q))
- __wake_up_locked_key(q, TASK_NORMAL, key);
- spin_unlock_irqrestore(&q->lock, flags);
-}
-EXPORT_SYMBOL(abort_exclusive_wait);
-
int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
{
int ret = default_wake_function(wait, mode, sync, key);
@@ -438,20 +407,29 @@ int __sched
__wait_on_bit_lock(wait_queue_head_t *wq, struct wait_bit_queue *q,
wait_bit_action_f *action, unsigned mode)
{
- do {
- int ret;
+ int ret = 0;

+ for (;;) {
prepare_to_wait_exclusive(wq, &q->wait, mode);
- if (!test_bit(q->key.bit_nr, q->key.flags))
- continue;
- ret = action(&q->key, mode);
- if (!ret)
- continue;
- 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);
- return 0;
+ if (test_bit(q->key.bit_nr, q->key.flags)) {
+ ret = action(&q->key, mode);
+ /*
+ * See the comment in prepare_to_wait_event().
+ * finish_wait() does not necessarily takes wq->lock,
+ * but test_and_set_bit() implies mb() which pairs with
+ * smp_mb__after_atomic() before wake_up_page().
+ */
+ if (ret)
+ finish_wait(wq, &q->wait);
+ }
+ if (!test_and_set_bit(q->key.bit_nr, q->key.flags)) {
+ if (!ret)
+ finish_wait(wq, &q->wait);
+ return 0;
+ } else if (ret) {
+ return ret;
+ }
+ }
}
EXPORT_SYMBOL(__wait_on_bit_lock);

\
 
 \ /
  Last update: 2016-09-30 13:59    [W:0.084 / U:0.196 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site