xen/gntdevt: Fix race condition in gntdev_release()

While gntdev_release() is called the MMU notifier is still registered
and can traverse priv->maps list even if no pages are mapped (which is
the case -- gntdev_release() is called after all). But
gntdev_release() will clear that list, so make sure that only one of
those things happens at the same time.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 67b9163db718..0dbb222daaf1 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -568,12 +568,14 @@ static int gntdev_release(struct inode *inode, struct file *flip)
 
         pr_debug("priv %p\n", priv);
 
+        mutex_lock(&priv->lock);
         while (!list_empty(&priv->maps)) {
                 map = list_entry(priv->maps.next, struct grant_map, next);
                 list_del(&map->next);
                 gntdev_put_map(NULL /* already removed */, map);
         }
         WARN_ON(!list_empty(&priv->freeable_maps));
+        mutex_unlock(&priv->lock);
 
         if (use_ptemod)
                 mmu_notifier_unregister(&priv->mn, priv->mm);