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| author | Michael S. Tsirkin <mst@redhat.com> | 2013-07-09 13:19:18 +0300 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2013-08-02 22:14:52 +0200 |
| commit | f5615a4ebd1ac0709a44e5fd2f638005919d71ac (patch) | |
| tree | c92d49704fe53e2b0eaec5f4d4e0685ad98de7dd | |
| parent | 1e079ec5c16199e63c9c5e0e346a0fdf47681f32 (diff) | |
| download | lwn-f5615a4ebd1ac0709a44e5fd2f638005919d71ac.tar.gz lwn-f5615a4ebd1ac0709a44e5fd2f638005919d71ac.zip | |
virtio_net: fix race in RX VQ processing
commit cbdadbbf0c790f79350a8f36029208944c5487d0 upstream.
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>
Signed-off-by: David S. Miller <davem@davemloft.net>
[wg: Backported to 3.2]
Signed-off-by: Wolfram Gloger <wmglo@dent.med.uni-muenchen.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
| -rw-r--r-- | drivers/net/virtio_net.c | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 6ee8410443c4..43a6a11d261d 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -508,7 +508,7 @@ static int virtnet_poll(struct napi_struct *napi, int budget) { struct virtnet_info *vi = container_of(napi, struct virtnet_info, napi); void *buf; - unsigned int len, received = 0; + unsigned int r, len, received = 0; again: while (received < budget && @@ -525,8 +525,9 @@ again: /* Out of packets? */ if (received < budget) { + r = virtqueue_enable_cb_prepare(vi->rvq); napi_complete(napi); - if (unlikely(!virtqueue_enable_cb(vi->rvq)) && + if (unlikely(virtqueue_poll(vi->rvq, r)) && napi_schedule_prep(napi)) { virtqueue_disable_cb(vi->rvq); __napi_schedule(napi); |