pve-edge-kernel/patches/kernel/0022-sched-wait-Fix-add_wait_queue-behavioral-change.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Omar Sandoval <[email protected]>
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 <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
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 <[email protected]>
(cherry picked from commit c6b9d9a33029014446bd9ed84c1688f6d3d4eab9)
Signed-off-by: Fabian Grünbichler <[email protected]>
---
 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