FAILED: patch "[PATCH] io_uring/poll: fix signed comparison in" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 326941b22806cbf2df1fbfe902b7908b368cce42
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026050147-vitality-crayfish-d8e1@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 326941b22806cbf2df1fbfe902b7908b368cce42 Mon Sep 17 00:00:00 2001
From: Longxuan Yu <ylong030@ucr.edu>
Date: Sun, 12 Apr 2026 16:38:20 +0800
Subject: [PATCH] io_uring/poll: fix signed comparison in
 io_poll_get_ownership()

io_poll_get_ownership() uses a signed comparison to check whether
poll_refs has reached the threshold for the slowpath:

    if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))

atomic_read() returns int (signed). When IO_POLL_CANCEL_FLAG
(BIT(31)) is set in poll_refs, the value becomes negative in
signed arithmetic, so the >= 128 comparison always evaluates to
false and the slowpath is never taken.

Fix this by casting the atomic_read() result to unsigned int
before the comparison, so that the cancel flag is treated as a
large positive value and correctly triggers the slowpath.

Fixes: a26a35e9019f ("io_uring: make poll refs more robust")
Cc: stable@vger.kernel.org
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Co-developed-by: Yuan Tan <yuantan098@gmail.com>
Signed-off-by: Yuan Tan <yuantan098@gmail.com>
Suggested-by: Xin Liu <bird@lzu.edu.cn>
Tested-by: Zhengchuan Liang <zcliangcn@gmail.com>
Signed-off-by: Longxuan Yu <ylong030@ucr.edu>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://patch.msgid.link/3a3508b08bcd7f1bc3beff848ae6e1d73d355043.1775965597.git.ylong030@ucr.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/poll.c b/io_uring/poll.c
index 74eef7884159..6834e2db937e 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -93,7 +93,7 @@ static bool io_poll_get_ownership_slowpath(struct io_kiocb *req)
  */
 static inline bool io_poll_get_ownership(struct io_kiocb *req)
 {
-	if (unlikely(atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))
+	if (unlikely((unsigned int)atomic_read(&req->poll_refs) >= IO_POLL_REF_BIAS))
 		return io_poll_get_ownership_slowpath(req);
 	return !(atomic_fetch_inc(&req->poll_refs) & IO_POLL_REF_MASK);
 }