[PATCH 4.16 48/68] xen: xenbus_dev_frontend: Fix XS_TRANSACTION_END handling

From: Greg Kroah-Hartman
Date: Tue Apr 17 2018 - 12:01:59 EST

4.16-stable review patch. If anyone has any objections, please let me know.


From: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx> # 4.11
Fixes: fd8aa9095a95 ("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Signed-off-by: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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;