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cherry-pick sched-wait bug fix

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(included in 4.15 and queued for 4.14)
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Fabian Grünbichler 2018-02-13 12:35:13 +01:00
parent d320e5b2c3
commit ef812b062d
1 changed files with 52 additions and 0 deletions
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patches/kernel/0022-sched-wait-Fix-add_wait_queue-behavioral-change.patch Normal file
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@ -0,0 +1,52 @@
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Omar Sandoval <osandov@fb.com>
Date: Tue, 5 Dec 2017 23:15:31 -0800
Subject: [PATCH] sched/wait: Fix add_wait_queue() behavioral change
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
The following cleanup commit:
50816c48997a ("sched/wait: Standardize internal naming of wait-queue entries")
... unintentionally changed the behavior of add_wait_queue() from
inserting the wait entry at the head of the wait queue to the tail
of the wait queue.
Beyond a negative performance impact this change in behavior
theoretically also breaks wait queues which mix exclusive and
non-exclusive waiters, as non-exclusive waiters will not be
woken up if they are queued behind enough exclusive waiters.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@fb.com
Fixes: ("sched/wait: Standardize internal naming of wait-queue entries")
Link: http://lkml.kernel.org/r/a16c8ccffd39bd08fdaa45a5192294c784b803a7.1512544324.git.osandov@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit c6b9d9a33029014446bd9ed84c1688f6d3d4eab9)
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
---
kernel/sched/wait.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c
index d6afed6d0752..c09ebe92a40a 100644
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -27,7 +27,7 @@ void add_wait_queue(struct wait_queue_head *wq_head, struct wait_queue_entry *wq
wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&wq_head->lock, flags);
- __add_wait_queue_entry_tail(wq_head, wq_entry);
+ __add_wait_queue(wq_head, wq_entry);
spin_unlock_irqrestore(&wq_head->lock, flags);
}
EXPORT_SYMBOL(add_wait_queue);
--
2.14.2