From b0c057ca7e835b36c6050c7627634b664796c1d6 Mon Sep 17 00:00:00 2001
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: Thu, 13 Feb 2014 11:45:11 +0200
Subject: [PATCH] vhost: fix a theoretical race in device cleanup

vhost_zerocopy_callback accesses VQ right after it drops a ubuf
reference.  In theory, this could race with device removal which waits
on the ubuf kref, and crash on use after free.

Do all accesses within rcu read side critical section, and synchronize
on release.

Since callbacks are always invoked from bh, synchronize_rcu_bh seems
enough and will help release complete a bit faster.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
Reading git-format-patch failed