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    Subject[PATCH 5.10 176/243] virtio_net: move tx vq operation under tx queue lock
    Date
    From: Michael S. Tsirkin <mst@redhat.com>

    [ Upstream commit 5a2f966d0f3fa0ef6dada7ab9eda74cacee96b8a ]

    It's unsafe to operate a vq from multiple threads.
    Unfortunately this is exactly what we do when invoking
    clean tx poll from rx napi.
    Same happens with napi-tx even without the
    opportunistic cleaning from the receive interrupt: that races
    with processing the vq in start_xmit.

    As a fix move everything that deals with the vq to under tx lock.

    Fixes: b92f1e6751a6 ("virtio-net: transmit napi")
    Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/net/virtio_net.c | 22 +++++++++++++++++++++-
    1 file changed, 21 insertions(+), 1 deletion(-)

    diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
    index 345a0f51e8d7..7d1f609306f9 100644
    --- a/drivers/net/virtio_net.c
    +++ b/drivers/net/virtio_net.c
    @@ -1519,6 +1519,8 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
    struct virtnet_info *vi = sq->vq->vdev->priv;
    unsigned int index = vq2txq(sq->vq);
    struct netdev_queue *txq;
    + int opaque;
    + bool done;

    if (unlikely(is_xdp_raw_buffer_queue(vi, index))) {
    /* We don't need to enable cb for XDP */
    @@ -1528,10 +1530,28 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)

    txq = netdev_get_tx_queue(vi->dev, index);
    __netif_tx_lock(txq, raw_smp_processor_id());
    + virtqueue_disable_cb(sq->vq);
    free_old_xmit_skbs(sq, true);
    +
    + opaque = virtqueue_enable_cb_prepare(sq->vq);
    +
    + done = napi_complete_done(napi, 0);
    +
    + if (!done)
    + virtqueue_disable_cb(sq->vq);
    +
    __netif_tx_unlock(txq);

    - virtqueue_napi_complete(napi, sq->vq, 0);
    + if (done) {
    + if (unlikely(virtqueue_poll(sq->vq, opaque))) {
    + if (napi_schedule_prep(napi)) {
    + __netif_tx_lock(txq, raw_smp_processor_id());
    + virtqueue_disable_cb(sq->vq);
    + __netif_tx_unlock(txq);
    + __napi_schedule(napi);
    + }
    + }
    + }

    if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
    netif_tx_wake_queue(txq);
    --
    2.30.2


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