* Jens Axboe axboe@kernel.dk 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@kernel.org
Thanks,
Ingo
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From c6b9d9a33029014446bd9ed84c1688f6d3d4eab9 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
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... Signed-off-by: Ingo Molnar mingo@kernel.org --- 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);