xenbus: req->err should be updated before req->state

This patch adds the barrier to guarantee that req->err is always updated
before req->state.

Otherwise, read_reply() would not return ERR_PTR(req->err) but
req->body, when process_writes()->xb_write() is failed.

Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
Link: https://lore.kernel.org/r/20200303221423.21962-2-dongli.zhang@oracle.com
Reviewed-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index 852ed16..eb5151f 100644 (file)
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -397,6 +397,8 @@ static int process_writes(void)
        if (state.req->state == xb_req_state_aborted)
                kfree(state.req);
        else {
+               /* write err, then update state */
+               virt_wmb();
                state.req->state = xb_req_state_got_reply;
                wake_up(&state.req->wq);
        }