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    Subject[PATCH 5.9 124/133] io_uring: fix link lookup racing with link timeout
    Date
    From: Pavel Begunkov <asml.silence@gmail.com>

    commit 9a472ef7a3690ac0b77ebfb04c88fa795de2adea upstream.

    We can't just go over linked requests because it may race with linked
    timeouts. Take ctx->completion_lock in that case.

    Cc: stable@vger.kernel.org # v5.7+
    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 | 16 +++++++++++++++-
    1 file changed, 15 insertions(+), 1 deletion(-)

    --- a/fs/io_uring.c
    +++ b/fs/io_uring.c
    @@ -8176,7 +8176,21 @@ static bool io_timeout_remove_link(struc

    static bool io_cancel_link_cb(struct io_wq_work *work, void *data)
    {
    - return io_match_link(container_of(work, struct io_kiocb, work), data);
    + struct io_kiocb *req = container_of(work, struct io_kiocb, work);
    + bool ret;
    +
    + if (req->flags & REQ_F_LINK_TIMEOUT) {
    + unsigned long flags;
    + struct io_ring_ctx *ctx = req->ctx;
    +
    + /* protect against races with linked timeouts */
    + spin_lock_irqsave(&ctx->completion_lock, flags);
    + ret = io_match_link(req, data);
    + spin_unlock_irqrestore(&ctx->completion_lock, flags);
    + } else {
    + ret = io_match_link(req, data);
    + }
    + return ret;
    }

    static void io_attempt_cancel(struct io_ring_ctx *ctx, struct io_kiocb *req)

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