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virtio-net: don't re-enable refill work too early when NAPI is disabled

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Commit 4bc12818b3 ("virtio-net: disable delayed refill when pausing rx")
fixed a deadlock between reconfig paths and refill work trying to disable
the same NAPI instance. The refill work can't run in parallel with reconfig
because trying to double-disable a NAPI instance causes a stall under the
instance lock, which the reconfig path needs to re-enable the NAPI and
therefore unblock the stalled thread.

There are two cases where we re-enable refill too early. One is in the
virtnet_set_queues() handler. We call it when installing XDP:

   virtnet_rx_pause_all(vi);
   ...
   virtnet_napi_tx_disable(..);
   ...
   virtnet_set_queues(..);
   ...
   virtnet_rx_resume_all(..);

We want the work to be disabled until we call virtnet_rx_resume_all(),
but virtnet_set_queues() kicks it before NAPIs were re-enabled.

The other case is a more trivial case of mis-ordering in
__virtnet_rx_resume() found by code inspection.

Taking the spin lock in virtnet_set_queues() (requested during review)
may be unnecessary as we are under rtnl_lock and so are all paths writing
to ->refill_enabled.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Bui Quang Minh <minhquangbui99@gmail.com>
Fixes: 4bc12818b3 ("virtio-net: disable delayed refill when pausing rx")
Fixes: 413f0271f3 ("net: protect NAPI enablement with netdev_lock()")
Link: https://patch.msgid.link/20250430163758.3029367-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski
2025-04-30 09:37:58 -07:00
parent 75dbdaad32
commit 1e20324b23
1 changed files with 8 additions and 3 deletions
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11
drivers/net/virtio_net.c
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@@ -3383,12 +3383,15 @@ static void __virtnet_rx_resume(struct virtnet_info *vi,
bool refill)
{
bool running = netif_running(vi->dev);
bool schedule_refill = false;
if (refill && !try_fill_recv(vi, rq, GFP_KERNEL))
schedule_delayed_work(&vi->refill, 0);
schedule_refill = true;
if (running)
virtnet_napi_enable(rq);
if (schedule_refill)
schedule_delayed_work(&vi->refill, 0);
}
static void virtnet_rx_resume_all(struct virtnet_info *vi)
@@ -3728,8 +3731,10 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
succ:
vi->curr_queue_pairs = queue_pairs;
/* virtnet_open() will refill when device is going to up. */
if (dev->flags & IFF_UP)
spin_lock_bh(&vi->refill_lock);
if (dev->flags & IFF_UP && vi->refill_enabled)
schedule_delayed_work(&vi->refill, 0);
spin_unlock_bh(&vi->refill_lock);
return 0;
}