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Tsirkin" To: Jason Wang Cc: Jakub Kicinski , davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, horms@kernel.org, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, minhquangbui99@gmail.com, romieu@fr.zoreil.com, kuniyu@amazon.com, virtualization@lists.linux.dev Subject: Re: [PATCH net] virtio-net: don't re-enable refill work too early when NAPI is disabled Message-ID: <20250430012856-mutt-send-email-mst@kernel.org> References: <20250429143104.2576553-1-kuba@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Apr 30, 2025 at 11:49:15AM +0800, Jason Wang wrote: > On Tue, Apr 29, 2025 at 10:31 PM Jakub Kicinski wrote: > > > > Commit 4bc12818b363 ("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. > > > > Fixes: 4bc12818b363 ("virtio-net: disable delayed refill when pausing rx") > > Fixes: 413f0271f396 ("net: protect NAPI enablement with netdev_lock()") > > Signed-off-by: Jakub Kicinski > > --- > > CC: mst@redhat.com > > CC: jasowang@redhat.com > > CC: xuanzhuo@linux.alibaba.com > > CC: eperezma@redhat.com > > CC: minhquangbui99@gmail.com > > CC: romieu@fr.zoreil.com > > CC: kuniyu@amazon.com > > CC: virtualization@lists.linux.dev > > --- > > drivers/net/virtio_net.c | 9 ++++++--- > > 1 file changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 848fab51dfa1..4c904e176495 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -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) > > @@ -3728,7 +3731,7 @@ 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) > > + if (dev->flags & IFF_UP && vi->refill_enabled) > > schedule_delayed_work(&vi->refill, 0); > > This has the assumption that the toggle of the refill_enabled is under > RTNL. Though it's true now but it looks to me it's better to protect > it against refill_lock. > > Thanks Good point. > > > > return 0; > > -- > > 2.49.0 > >