From: "Michael S. Tsirkin" <mst@redhat.com>
To: linux-kernel@vger.kernel.org
Cc: netdev@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: [PATCH v2 2/2] virtio_net: fix race in RX VQ processing
Date: Tue, 9 Jul 2013 08:13:04 +0300 [thread overview]
Message-ID: <1373346713-442-3-git-send-email-mst@redhat.com> (raw)
In-Reply-To: <1373346713-442-1-git-send-email-mst@redhat.com>
virtio net called virtqueue_enable_cq on RX path after napi_complete, so
with NAPI_STATE_SCHED clear - outside the implicit napi lock.
This violates the requirement to synchronize virtqueue_enable_cq wrt
virtqueue_add_buf. In particular, used event can move backwards,
causing us to lose interrupts.
In a debug build, this can trigger panic within START_USE.
Jason Wang reports that he can trigger the races artificially,
by adding udelay() in virtqueue_enable_cb() after virtio_mb().
However, we must call napi_complete to clear NAPI_STATE_SCHED before
polling the virtqueue for used buffers, otherwise napi_schedule_prep in
a callback will fail, causing us to lose RX events.
To fix, call virtqueue_enable_cb_prepare with NAPI_STATE_SCHED
set (under napi lock), later call virtqueue_poll with
NAPI_STATE_SCHED clear (outside the lock).
Reported-by: Jason Wang <jasowang@redhat.com>
Tested-by: Jason Wang <jasowang@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
drivers/net/virtio_net.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 5305bd1..27f79dd 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -605,7 +605,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
container_of(napi, struct receive_queue, napi);
struct virtnet_info *vi = rq->vq->vdev->priv;
void *buf;
- unsigned int len, received = 0;
+ unsigned int r, len, received = 0;
again:
while (received < budget &&
@@ -622,8 +622,9 @@ again:
/* Out of packets? */
if (received < budget) {
+ r = virtqueue_enable_cb_prepare(rq->vq);
napi_complete(napi);
- if (unlikely(!virtqueue_enable_cb(rq->vq)) &&
+ if (unlikely(virtqueue_poll(rq->vq, r)) &&
napi_schedule_prep(napi)) {
virtqueue_disable_cb(rq->vq);
__napi_schedule(napi);
--
MST
next prev parent reply other threads:[~2013-07-09 5:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-07-09 5:12 [PATCH v2 0/2] virtio_net: fix race in RX VQ processing Michael S. Tsirkin
2013-07-09 5:13 ` Michael S. Tsirkin [this message]
2013-07-09 9:32 ` David Miller
2013-07-09 10:21 ` Michael S. Tsirkin
2013-07-09 10:19 ` [PATCH v2 1/2] virtio: support unlocked queue poll Michael S. Tsirkin
2013-07-09 19:46 ` [PATCH v2 0/2] virtio_net: fix race in RX VQ processing David Miller
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