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Date:   Mon,  7 Sep 2020 18:52:19 +0800
From:   Zhu Lingshan <lingshan.zhu@...el.com>
To:     jasowang@...hat.com, mst@...hat.com
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, Zhu Lingshan <lingshan.zhu@...el.com>
Subject: [PATCH 1/2] vhost: remove mutex ops in vhost_set_backend_features

In vhost_vdpa ioctl SET_BACKEND_FEATURES path, currect code
would try to acquire vhost dev mutex twice
(first shown in vhost_vdpa_unlocked_ioctl), which can lead
to a dead lock issue.
This commit removed mutex operations in vhost_set_backend_features.
As a compensation for vhost_net, a followinig commit will add
needed mutex lock/unlock operations in a new function
vhost_net_set_backend_features() which is a wrap of
vhost_set_backend_features().

Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
---
 drivers/vhost/vhost.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b45519ca66a7..e03c9e6f058f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2591,14 +2591,12 @@ void vhost_set_backend_features(struct vhost_dev *dev, u64 features)
 	struct vhost_virtqueue *vq;
 	int i;
 
-	mutex_lock(&dev->mutex);
 	for (i = 0; i < dev->nvqs; ++i) {
 		vq = dev->vqs[i];
 		mutex_lock(&vq->mutex);
 		vq->acked_backend_features = features;
 		mutex_unlock(&vq->mutex);
 	}
-	mutex_unlock(&dev->mutex);
 }
 EXPORT_SYMBOL_GPL(vhost_set_backend_features);
 
-- 
2.18.4

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