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

[Jens Axboe <axboe@kernel.dk>]

[-- Attachment #1: Type: text/plain, Size: 853 bytes --]

On 5/1/26 5:08 AM, gregkh@linuxfoundation.org wrote:
> 
> 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^..

Here's a version of that for 5.15 AND 5.10-stable, please apply for both.

-- 
Jens Axboe

[-- Attachment #2: 0001-io_uring-poll-fix-signed-comparison-in-io_poll_get_o.patch --]
[-- Type: text/x-patch, Size: 2202 bytes --]

From 4f1ddce4042ea4b3d8a3d14d1b4745d408b68090 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()

Commit 326941b22806cbf2df1fbfe902b7908b368cce42 usptream.

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>
---
 io_uring/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index cb54ebda0a8a..bc0f1a4980ee 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -5525,7 +5525,7 @@ 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);
 }
-- 
2.53.0