From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean-Philippe Brucker Subject: [PATCH] vhost: fix IOTLB locking Date: Fri, 30 Nov 2018 11:37:02 +0000 Message-ID: <20181130113702.1565-1-jean-philippe.brucker@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: mst@redhat.com, jasowang@redhat.com Cc: netdev@vger.kernel.org, davem@davemloft.net, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org 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. As long as we hold dev->mutex to prevent an ioctl from modifying vq->poll concurrently, we can safely call vhost_poll_queue() without holding vq->mutex. Since vhost_process_iotlb_msg() holds dev->mutex when calling vhost_iotlb_notify_vq(), avoid the deadlock by not taking vq->mutex. Fixes: 78139c94dc8c ("net: vhost: lock the vqs one by one") Signed-off-by: Jean-Philippe Brucker --- drivers/vhost/vhost.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 3a5f81a66d34..1cbb17f898f7 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -944,10 +944,10 @@ 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); + /* Safe to call outside vq->mutex as long as dev->mutex + * is held. + */ vhost_poll_queue(&node->vq->poll); - mutex_unlock(&node->vq->mutex); - list_del(&node->node); kfree(node); } -- 2.19.1