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    Subject[PATCH 6.0 013/862] io_uring/rw: fix unexpected link breakage
    Date
    From: Pavel Begunkov <asml.silence@gmail.com>

    commit bf68b5b34311ee57ed40749a1257a30b46127556 upstream.

    req->cqe.res is set in io_read() to the amount of bytes left to be done,
    which is used to figure out whether to fail a read or not. However,
    io_read() may do another without returning, and we stash the previous
    value into ->bytes_done but forget to update cqe.res. Then we ask a read
    to do strictly less than cqe.res but expect the return to be exactly
    cqe.res.

    Fix the bug by updating cqe.res for retries.

    Cc: stable@vger.kernel.org
    Reported-and-Tested-by: Beld Zhang <beldzhang@gmail.com>
    Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
    Link: https://lore.kernel.org/r/3a1088440c7be98e5800267af922a67da0ef9f13.1664235732.git.asml.silence@gmail.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    io_uring/rw.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/io_uring/rw.c
    +++ b/io_uring/rw.c
    @@ -823,6 +823,7 @@ int io_read(struct io_kiocb *req, unsign
    return -EAGAIN;
    }

    + req->cqe.res = iov_iter_count(&s->iter);
    /*
    * Now retry read with the IOCB_WAITQ parts set in the iocb. If
    * we get -EIOCBQUEUED, then we'll get a notification when the

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