[PATCH 5.10 510/717] io_uring: fix io_cqring_events()s noflush

Greg Kroah-Hartman
2020-12-28T14:46:42Z

From: Pavel Begunkov <asml.silence@gmail.com>

commit 59850d226e4907a6f37c1d2fe5ba97546a8691a4 upstream.

Checking !list_empty(&ctx->cq_overflow_list) around noflush in
io_cqring_events() is racy, because if it fails but a request overflowed
just after that, io_cqring_overflow_flush() still will be called.

Remove the second check, it shouldn't be a problem for performance,
because there is cq_check_overflow bit check just above.

Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2242,7 +2242,7 @@ static unsigned io_cqring_events(struct
* we wake up the task, and the next invocation will flush the
* entries. We cannot safely to it from here.
*/
- if (noflush && !list_empty(&ctx->cq_overflow_list))
+ if (noflush)
return -1U;

io_cqring_overflow_flush(ctx, false, NULL, NULL);