Re: [PATCH v2] vhost: fix IOTLB locking

[David Miller]

From: Jean-Philippe Brucker 
Date: Fri, 30 Nov 2018 16:05:53 +

> 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 
> Acked-by: Michael S. Tsirkin 
> Signed-off-by: Jean-Philippe Brucker 

Applied, thank you.
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[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 
Acked-by: Michael S. Tsirkin 
Signed-off-by: Jean-Philippe Brucker 
---
 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(>vq->mutex);
vhost_poll_queue(>vq->poll);
-   mutex_unlock(>vq->mutex);
-
list_del(>node);
kfree(node);
}
-- 
2.19.1

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