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vhost_net: switch to use mutex_trylock() in vhost_net_busy_poll() 

We used to hold the mutex of paired virtqueue in
vhost_net_busy_poll(). But this will results an inconsistent lock
order which may cause deadlock if we try to bring back the protection
of device IOTLB with vq mutex that requires to hold mutex of all
virtqueues at the same time.

Fix this simply by switching to use mutex_trylock(), when fail just
skip the busy polling. This can happen when device IOTLB is under
updating which should be rare.

Fixes: commit 78139c94dc ("net: vhost: lock the vqs one by one")
Cc: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Wang 2018-12-13 10:53:38 +08:00 committed by David S. Miller
parent 841df92241
commit 476e8ba712
1 changed files with 7 additions and 1 deletions
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8
drivers/vhost/net.c
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@ -513,7 +513,13 @@ static void vhost_net_busy_poll(struct vhost_net *net,
struct socket *sock;
struct vhost_virtqueue *vq = poll_rx ? tvq : rvq;
mutex_lock_nested(&vq->mutex, poll_rx ? VHOST_NET_VQ_TX: VHOST_NET_VQ_RX);
/* Try to hold the vq mutex of the paired virtqueue. We can't
* use mutex_lock() here since we could not guarantee a
* consistenet lock ordering.
*/
if (!mutex_trylock(&vq->mutex))
return;
vhost_disable_notify(&net->dev, vq);
sock = rvq->private_data;