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[V2,6/9] vhost: don't do synchronize_rcu() in vhost_uninit_vq_maps()

Message ID 20190731084655.7024-7-jasowang@redhat.com (mailing list archive)
State New, archived
Headers show
Series Fixes for metadata accelreation | expand

Commit Message

Jason Wang July 31, 2019, 8:46 a.m. UTC
There's no need for RCU synchronization in vhost_uninit_vq_maps()
since we've already serialized with readers (memory accessors). This
also avoid the possible userspace DOS through ioctl() because of the
possible high latency caused by synchronize_rcu().

Reported-by: Michael S. Tsirkin <mst@redhat.com>
Fixes: 7f466032dc9e ("vhost: access vq metadata through kernel virtual address")
Signed-off-by: Jason Wang <jasowang@redhat.com>
 drivers/vhost/vhost.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
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diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c12cdadb0855..cfc11f9ed9c9 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -333,7 +333,9 @@  static void vhost_uninit_vq_maps(struct vhost_virtqueue *vq)
-	synchronize_rcu();
+	/* No need for synchronize_rcu() or kfree_rcu() since we are
+	 * serialized with memory accessors (e.g vq mutex held).
+	 */
 	for (i = 0; i < VHOST_NUM_ADDRS; i++)
 		if (map[i])