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    Subject[PATCH 4.14 47/49] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Simon Gaiser <simon@invisiblethingslab.com>

    commit 2a22ee6c3ab1d761bc9c04f1e4117edd55b82f09 upstream.

    Commit fd8aa9095a95 ("xen: optimize xenbus driver for multiple
    concurrent xenstore accesses") made a subtle change to the semantic of
    xenbus_dev_request_and_reply() and xenbus_transaction_end().

    Before on an error response to XS_TRANSACTION_END
    xenbus_dev_request_and_reply() would not decrement the active
    transaction counter. But xenbus_transaction_end() has always counted the
    transaction as finished regardless of the response.

    The new behavior is that xenbus_dev_request_and_reply() and
    xenbus_transaction_end() will always count the transaction as finished
    regardless the response code (handled in xs_request_exit()).

    But xenbus_dev_frontend tries to end a transaction on closing of the
    device if the XS_TRANSACTION_END failed before. Trying to close the
    transaction twice corrupts the reference count. So fix this by also
    considering a transaction closed if we have sent XS_TRANSACTION_END once
    regardless of the return code.

    Cc: <stable@vger.kernel.org> # 4.11
    Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
    Signed-off-by: Simon Gaiser <simon@invisiblethingslab.com>
    Reviewed-by: Juergen Gross <jgross@suse.com>
    Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/xen/xenbus/xenbus_dev_frontend.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/xen/xenbus/xenbus_dev_frontend.c
    +++ b/drivers/xen/xenbus/xenbus_dev_frontend.c
    @@ -365,7 +365,7 @@ void xenbus_dev_queue_reply(struct xb_re
    if (WARN_ON(rc))
    goto out;
    }
    - } else if (req->msg.type == XS_TRANSACTION_END) {
    + } else if (req->type == XS_TRANSACTION_END) {
    trans = xenbus_get_transaction(u, req->msg.tx_id);
    if (WARN_ON(!trans))
    goto out;

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