Re: FAILED: patch "[PATCH] io_uring/poll: correctly handle io_poll_add() return value on" failed to apply to 6.12-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 12/29/25 5:22 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.12-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>.

Here's one for 6.12-stable.

-- 
Jens Axboe

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From a40f5a12d62f20ce2f9c3687b880218c09e0cd74 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Mon, 1 Dec 2025 13:25:22 -0700
Subject: [PATCH] io_uring/poll: correctly handle io_poll_add() return value on
 update

Commit 84230ad2d2afbf0c44c32967e525c0ad92e26b4e upstream.

When the core of io_uring was updated to handle completions
consistently and with fixed return codes, the POLL_REMOVE opcode
with updates got slightly broken. If a POLL_ADD is pending and
then POLL_REMOVE is used to update the events of that request, if that
update causes the POLL_ADD to now trigger, then that completion is lost
and a CQE is never posted.

Additionally, ensure that if an update does cause an existing POLL_ADD
to complete, that the completion value isn't always overwritten with
-ECANCELED. For that case, whatever io_poll_add() set the value to
should just be retained.

Cc: stable@vger.kernel.org
Fixes: 97b388d70b53 ("io_uring: handle completions in the core")
Reported-by: syzbot+641eec6b7af1f62f2b99@syzkaller.appspotmail.com
Tested-by: syzbot+641eec6b7af1f62f2b99@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/poll.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/io_uring/poll.c b/io_uring/poll.c
index bfdb537572f7..c833fd18d0ef 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -1038,12 +1038,17 @@ int io_poll_remove(struct io_kiocb *req, unsigned int issue_flags)
 
 		ret2 = io_poll_add(preq, issue_flags & ~IO_URING_F_UNLOCKED);
 		/* successfully updated, don't complete poll request */
-		if (!ret2 || ret2 == -EIOCBQUEUED)
+		if (ret2 == IOU_ISSUE_SKIP_COMPLETE)
 			goto out;
+		/* request completed as part of the update, complete it */
+		else if (ret2 == IOU_OK)
+			goto complete;
 	}
 
-	req_set_fail(preq);
 	io_req_set_res(preq, -ECANCELED, 0);
+complete:
+	if (preq->cqe.res < 0)
+		req_set_fail(preq);
 	preq->io_task_work.func = io_req_task_complete;
 	io_req_task_work_add(preq);
 out:
-- 
2.51.0