[PATCH 5.15 089/120] io_uring: fix tw losing poll events

Greg Kroah-Hartman
2022-12-05T19:39:45Z

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

[ upstream commit 539bcb57da2f58886d7d5c17134236b0ec9cd15d ]

We may never try to process a poll wake and its mask if there was
multiple wake ups racing for queueing up a tw. Force
io_poll_check_events() to update the mask by vfs_poll().

Cc: stable@vger.kernel.org
Fixes: aa43477b04025 ("io_uring: poll rework")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/00344d60f8b18907171178d7cf598de71d127b0b.1668710222.git.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 | 7 +++++++
1 file changed, 7 insertions(+)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5440,6 +5440,13 @@ static int io_poll_check_events(struct i
return 0;
if (v & IO_POLL_CANCEL_FLAG)
return -ECANCELED;
+ /*
+ * cqe.res contains only events of the first wake up
+ * and all others are be lost. Redo vfs_poll() to get
+ * up to date state.
+ */
+ if ((v & IO_POLL_REF_MASK) != 1)
+ req->result = 0;

if (!req->result) {
struct poll_table_struct pt = { ._key = poll->events };