Commit e1d6fbc3 authored by David S. Miller's avatar David S. Miller
Browse files

virtio_net: fix race in RX VQ processing

Michael S. Tsirkin says:

====================
Jason Wang reported a race in RX VQ processing:
virtqueue_enable_cb is called outside napi lock,
violating virtio serialization rules.
The race has been there from day 1, but it got especially nasty in 3.0
when commit a5c262c5


"virtio_ring: support event idx feature"
added more dependency on vq state.

Please review, and consider for 3.11 and stable.

Changes from v1:
	- Added Jason's Tested-by tag
	- minor coding style fix
====================
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 01276ed2 cbdadbbf
......@@ -602,7 +602,7 @@ 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 &&
......@@ -619,8 +619,9 @@ 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);
......
......@@ -607,19 +607,21 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
/**
* virtqueue_enable_cb - restart callbacks after disable_cb.
* virtqueue_enable_cb_prepare - restart callbacks after disable_cb
* @vq: the struct virtqueue we're talking about.
*
* This re-enables callbacks; it returns "false" if there are pending
* buffers in the queue, to detect a possible race between the driver
* checking for more work, and enabling callbacks.
* This re-enables callbacks; it returns current queue state
* in an opaque unsigned value. This value should be later tested by
* virtqueue_poll, to detect a possible race between the driver checking for
* more work, and enabling callbacks.
*
* Caller must ensure we don't call this with other virtqueue
* operations at the same time (except where noted).
*/
bool virtqueue_enable_cb(struct virtqueue *_vq)
unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
{
struct vring_virtqueue *vq = to_vvq(_vq);
u16 last_used_idx;
START_USE(vq);
......@@ -629,15 +631,45 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
* either clear the flags bit or point the event index at the next
* entry. Always do both to keep code simple. */
vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
vring_used_event(&vq->vring) = vq->last_used_idx;
vring_used_event(&vq->vring) = last_used_idx = vq->last_used_idx;
END_USE(vq);
return last_used_idx;
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
/**
* virtqueue_poll - query pending used buffers
* @vq: the struct virtqueue we're talking about.
* @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare).
*
* Returns "true" if there are pending used buffers in the queue.
*
* This does not need to be serialized.
*/
bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx)
{
struct vring_virtqueue *vq = to_vvq(_vq);
virtio_mb(vq->weak_barriers);
if (unlikely(more_used(vq))) {
END_USE(vq);
return false;
}
return (u16)last_used_idx != vq->vring.used->idx;
}
EXPORT_SYMBOL_GPL(virtqueue_poll);
END_USE(vq);
return true;
/**
* virtqueue_enable_cb - restart callbacks after disable_cb.
* @vq: the struct virtqueue we're talking about.
*
* This re-enables callbacks; it returns "false" if there are pending
* buffers in the queue, to detect a possible race between the driver
* checking for more work, and enabling callbacks.
*
* Caller must ensure we don't call this with other virtqueue
* operations at the same time (except where noted).
*/
bool virtqueue_enable_cb(struct virtqueue *_vq)
{
unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq);
return !virtqueue_poll(_vq, last_used_idx);
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
......
......@@ -70,6 +70,10 @@ void virtqueue_disable_cb(struct virtqueue *vq);
bool virtqueue_enable_cb(struct virtqueue *vq);
unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
bool virtqueue_poll(struct virtqueue *vq, unsigned);
bool virtqueue_enable_cb_delayed(struct virtqueue *vq);
void *virtqueue_detach_unused_buf(struct virtqueue *vq);
......
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