Re: FAILED: patch "[PATCH] io_uring: move local task_work in exit cancel loop" failed to apply to 6.6-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 1/19/26 4:47 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.6-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
> git checkout FETCH_HEAD
> git cherry-pick -x da579f05ef0faada3559e7faddf761c75cdf85e1
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026011956-unclog-language-54ed@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

6.12 variant also applies to 6.6, attached again here for 6.6-stable.

-- 
Jens Axboe

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From ddde1e8955c4d7574af7f78ffa64695482de3fc8 Mon Sep 17 00:00:00 2001
From: Ming Lei <ming.lei@redhat.com>
Date: Wed, 14 Jan 2026 16:54:05 +0800
Subject: [PATCH] io_uring: move local task_work in exit cancel loop

Commit da579f05ef0faada3559e7faddf761c75cdf85e1 upstream.

With IORING_SETUP_DEFER_TASKRUN, task work is queued to ctx->work_llist
(local work) rather than the fallback list. During io_ring_exit_work(),
io_move_task_work_from_local() was called once before the cancel loop,
moving work from work_llist to fallback_llist.

However, task work can be added to work_llist during the cancel loop
itself. There are two cases:

1) io_kill_timeouts() is called from io_uring_try_cancel_requests() to
cancel pending timeouts, and it adds task work via io_req_queue_tw_complete()
for each cancelled timeout:

2) URING_CMD requests like ublk can be completed via
io_uring_cmd_complete_in_task() from ublk_queue_rq() during canceling,
given ublk request queue is only quiesced when canceling the 1st uring_cmd.

Since io_allowed_defer_tw_run() returns false in io_ring_exit_work()
(kworker != submitter_task), io_run_local_work() is never invoked,
and the work_llist entries are never processed. This causes
io_uring_try_cancel_requests() to loop indefinitely, resulting in
100% CPU usage in kworker threads.

Fix this by moving io_move_task_work_from_local() inside the cancel
loop, ensuring any work on work_llist is moved to fallback before
each cancel attempt.

Cc: stable@vger.kernel.org
Fixes: c0e0d6ba25f1 ("io_uring: add IORING_SETUP_DEFER_TASKRUN")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
(cherry picked from commit da579f05ef0faada3559e7faddf761c75cdf85e1)
---
 io_uring/io_uring.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index adf2b0a1bb59..99b0b1ba0fe2 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -2904,11 +2904,11 @@ static __cold void io_ring_exit_work(struct work_struct *work)
 			mutex_unlock(&ctx->uring_lock);
 		}
 
-		if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
-			io_move_task_work_from_local(ctx);
-
-		while (io_uring_try_cancel_requests(ctx, NULL, true))
+		do {
+			if (ctx->flags & IORING_SETUP_DEFER_TASKRUN)
+				io_move_task_work_from_local(ctx);
 			cond_resched();
+		} while (io_uring_try_cancel_requests(ctx, NULL, true));
 
 		if (ctx->sq_data) {
 			struct io_sq_data *sqd = ctx->sq_data;
-- 
2.51.0