vhost: use mutex_lock_nested() in vhost_dev_lock_vqs()

jasowang · davem330 · commit e9cb4239134c · 2018-01-24T16:55:37.000-05:00
We used to call mutex_lock() in vhost_dev_lock_vqs() which tries to hold mutexes of all virtqueues. This may confuse lockdep to report a possible deadlock because of trying to hold locks belong to same class. Switch to use mutex_lock_nested() to avoid false positive. Fixes: 6b1e6cc ("vhost: new device IOTLB API") Reported-by: syzbot+dbb7c1161485e61b0241@syzkaller.appspotmail.com Signed-off-by: Jason Wang <jasowang@redhat.com> Acked-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
@@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)
 {
 	int i = 0;
 	for (i = 0; i < d->nvqs; ++i)
-		mutex_lock(&d->vqs[i]->mutex);
+		mutex_lock_nested(&d->vqs[i]->mutex, i);
 }
 
 static void vhost_dev_unlock_vqs(struct vhost_dev *d)

Original file line number	Diff line number	Diff line change
`@@ -904,7 +904,7 @@ static void vhost_dev_lock_vqs(struct vhost_dev *d)`
`904`	`904`	`{`
`905`	`905`	`int i = 0;`
`906`	`906`	`for (i = 0; i < d->nvqs; ++i)`
`907`		`- mutex_lock(&d->vqs[i]->mutex);`
	`907`	`+ mutex_lock_nested(&d->vqs[i]->mutex, i);`
`908`	`908`	`}`
`909`	`909`
`910`	`910`	`static void vhost_dev_unlock_vqs(struct vhost_dev *d)`