[PATCH v2 1/1] io_uring/rw: fix downgraded mshot read

[PATCH v2 1/1] io_uring/rw: fix downgraded mshot read

[Pavel Begunkov]

The iowq path can downgrade a multishot request to the oneshot mode,
however io_read_mshot() doesn't handle that and would still post
multiple CQEs. That's not allowed, because io_req_post_cqe() requires
stricter context requirements.

The described can only happen with pollable files that don't support
FMODE_NOWAIT, which is an odd combination, so if even allowed it should
be fairly rare.

Cc: stable@vger.kernel.org
Reported-by: chase xd <sl1589472800@gmail.com>
Fixes: bee1d5becdf5b ("io_uring: disable io-wq execution of multishot NOWAIT requests")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

v2: inverse the if condition

 io_uring/rw.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/io_uring/rw.c b/io_uring/rw.c
index b1db4595788b..be176f4828e2 100644
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -1066,6 +1066,8 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
 		io_kbuf_recycle(req, issue_flags);
 		if (ret < 0)
 			req_set_fail(req);
+	} else if (!(req->flags & REQ_F_APOLL_MULTISHOT)) {
+		cflags = io_put_kbuf(req, ret, issue_flags);
 	} else {
 		/*
 		 * Any successful return value will keep the multishot read
-- 
2.47.1

Re: [PATCH v2 1/1] io_uring/rw: fix downgraded mshot read

[Jens Axboe]

On Sat, 28 Dec 2024 17:44:52 +0000, Pavel Begunkov wrote:
> The iowq path can downgrade a multishot request to the oneshot mode,
> however io_read_mshot() doesn't handle that and would still post
> multiple CQEs. That's not allowed, because io_req_post_cqe() requires
> stricter context requirements.
> 
> The described can only happen with pollable files that don't support
> FMODE_NOWAIT, which is an odd combination, so if even allowed it should
> be fairly rare.
> 
> [...]

Applied, thanks!

[1/1] io_uring/rw: fix downgraded mshot read
      commit: 38fc96a58ce40257aec79b32e9b310c86907c63c

Best regards,
-- 
Jens Axboe