[PATCH AUTOSEL 4.19 18/20] xenbus: req->err should be updated before req->state

[Sasha Levin]

From: Dongli Zhang <dongli.zhang@xxxxxxxxxx>

[ Upstream commit 8130b9d5b5abf26f9927b487c15319a187775f34 ]

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@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200303221423.21962-2-dongli.zhang@xxxxxxxxxx
Reviewed-by: Julien Grall <jgrall@xxxxxxxxxx>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/xen/xenbus/xenbus_comms.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index 852ed161fc2a7..eb5151fc8efab 100644
--- 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);
 	}
-- 
2.20.1