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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Pavel Begunkov <asml.silence@gmail.com>,
        Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.9 070/391] io_uring: dont set COMP_LOCKED if wont put
Date:   Tue,  3 Nov 2020 21:32:01 +0100
Message-Id: <20201103203351.972293956@linuxfoundation.org>
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From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit 368c5481ae7c6a9719c40984faea35480d9f4872 ]

__io_kill_linked_timeout() sets REQ_F_COMP_LOCKED for a linked timeout
even if it can't cancel it, e.g. it's already running. It not only races
with io_link_timeout_fn() for ->flags field, but also leaves the flag
set and so io_link_timeout_fn() may find it and decide that it holds the
lock. Hopefully, the second problem is potential.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 59ab8c5c2aaaa..50a7a99dad4ca 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1650,6 +1650,7 @@ static bool io_link_cancel_timeout(struct io_kiocb *req)
 
 	ret = hrtimer_try_to_cancel(&req->io->timeout.timer);
 	if (ret != -1) {
+		req->flags |= REQ_F_COMP_LOCKED;
 		io_cqring_fill_event(req, -ECANCELED);
 		io_commit_cqring(ctx);
 		req->flags &= ~REQ_F_LINK_HEAD;
@@ -1672,7 +1673,6 @@ static bool __io_kill_linked_timeout(struct io_kiocb *req)
 		return false;
 
 	list_del_init(&link->link_list);
-	link->flags |= REQ_F_COMP_LOCKED;
 	wake_ev = io_link_cancel_timeout(link);
 	req->flags &= ~REQ_F_LINK_TIMEOUT;
 	return wake_ev;
-- 
2.27.0