[PATCH v2] vhost: fix IOTLB locking

[PATCH v2] vhost: fix IOTLB locking

[Jean-Philippe Brucker]

Commit 78139c94dc8c ("net: vhost: lock the vqs one by one") moved the vq
lock to improve scalability, but introduced a possible deadlock in
vhost-iotlb. vhost_iotlb_notify_vq() now takes vq->mutex while holding
the device's IOTLB spinlock. And on the vhost_iotlb_miss() path, the
spinlock is taken while holding vq->mutex.

Since calling vhost_poll_queue() doesn't require any lock, avoid the
deadlock by not taking vq->mutex.

Fixes: 78139c94dc8c ("net: vhost: lock the vqs one by one")
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
 drivers/vhost/vhost.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3a5f81a66d34..6b98d8e3a5bf 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -944,10 +944,7 @@ static void vhost_iotlb_notify_vq(struct vhost_dev *d,
 		if (msg->iova <= vq_msg->iova &&
 		    msg->iova + msg->size - 1 >= vq_msg->iova &&
 		    vq_msg->type == VHOST_IOTLB_MISS) {
-			mutex_lock(&node->vq->mutex);
 			vhost_poll_queue(&node->vq->poll);
-			mutex_unlock(&node->vq->mutex);
-
 			list_del(&node->node);
 			kfree(node);
 		}
-- 
2.19.1

Re: [PATCH v2] vhost: fix IOTLB locking

[David Miller]

From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Date: Fri, 30 Nov 2018 16:05:53 +0000

> Commit 78139c94dc8c ("net: vhost: lock the vqs one by one") moved the vq
> lock to improve scalability, but introduced a possible deadlock in
> vhost-iotlb. vhost_iotlb_notify_vq() now takes vq->mutex while holding
> the device's IOTLB spinlock. And on the vhost_iotlb_miss() path, the
> spinlock is taken while holding vq->mutex.
> 
> Since calling vhost_poll_queue() doesn't require any lock, avoid the
> deadlock by not taking vq->mutex.
> 
> Fixes: 78139c94dc8c ("net: vhost: lock the vqs one by one")
> Acked-by: Jason Wang <jasowang@redhat.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>

Applied, thank you.