[PATCH 6.12 249/567] io_uring/poll: correctly handle io_poll_add() return value on update

Greg Kroah-Hartman
2026-01-06T17:29:44Z

From: Jens Axboe <axboe@kernel.dk>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
io_uring/poll.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -1038,12 +1038,17 @@ found:

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);