* Jens Axboe <axboe@xxxxxxxxx> wrote:
> On 2/10/18 7:14 AM, Tetsuo Handa wrote:
> > Recently, we are seeing I/O hungup reports.
> >
> > I don't know whether a regression introduced by commit 50816c48997af857
> > ("sched/wait: Standardize internal naming of wait-queue entries") is relevant.
> > But shouldn't we backport commit c6b9d9a330290144 ("sched/wait: Fix
> > add_wait_queue() behavioral change") to 4.13+ kernels anyway?
>
> Yes, it most certainly should!
Indeed, the bug was introduced in v4.13 and the fix was included in v4.15, but
it's missing from v4.13 and v4.14 - not sure how I missed that.
The fix (also attached below) applies cleanly to both v4.13 and v4.14:
Acked-by: Ingo Molnar <mingo@xxxxxxxxxx>
Thanks,
Ingo
===================>
>From c6b9d9a33029014446bd9ed84c1688f6d3d4eab9 Mon Sep 17 00:00:00 2001
From: Omar Sandoval <osandov@xxxxxx>
Date: Tue, 5 Dec 2017 23:15:31 -0800
Subject: [PATCH] sched/wait: Fix add_wait_queue() behavioral change
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@xxxxxx>
Reviewed-by: Jens Axboe <axboe@xxxxxxxxx>
Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: kernel-team@xxxxxx
Fixes: ("sched/wait: Standardize internal naming of wait-queue entries")
Link: http://lkml.kernel.org/r/a16c8ccffd39bd08fdaa45a5192294c784b803a7.1512544324.git.osandov@xxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 98feab7933c7..929ecb7d6b78 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);