linux-kernel - [PATCH 5.15 19/73] io_uring: remove poll entry from list when canceling all

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Date:   Fri,  2 Sep 2022 14:18:43 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dylan Yudaken <dylany@...com>, Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [PATCH 5.15 19/73] io_uring: remove poll entry from list when canceling all

From: Jens Axboe <axboe@...nel.dk>

[ upstream commmit 61bc84c4008812d784c398cfb54118c1ba396dfc ]

When the ring is exiting, as part of the shutdown, poll requests are
removed. But io_poll_remove_all() does not remove entries when finding
them, and since completions are done out-of-band, we can find and remove
the same entry multiple times.

We do guard the poll execution by poll ownership, but that does not
exclude us from reissuing a new one once the previous removal ownership
goes away.

This can race with poll execution as well, where we then end up seeing
req->apoll be NULL because a previous task_work requeue finished the
request.

Remove the poll entry when we find it and get ownership of it. This
prevents multiple invocations from finding it.

Fixes: aa43477b0402 ("io_uring: poll rework")
Reported-by: Dylan Yudaken <dylany@...com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
[pavel: backport]
Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/io_uring.c |    1 +
 1 file changed, 1 insertion(+)

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5720,6 +5720,7 @@ static bool io_poll_remove_all(struct io
 		list = &ctx->cancel_hash[i];
 		hlist_for_each_entry_safe(req, tmp, list, hash_node) {
 			if (io_match_task_safe(req, tsk, cancel_all)) {
+				hlist_del_init(&req->hash_node);
 				io_poll_cancel_req(req);
 				found = true;
 			}