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 <jean-philippe.brucker@xxxxxxx>
---
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
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