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[68.197.162.46]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-474721bf582sm61201591cf.37.2025.03.03.10.33.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Mar 2025 10:33:12 -0800 (PST) Date: Mon, 3 Mar 2025 13:33:10 -0500 From: Joe Damato To: Jakub Kicinski , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, gerhard@engleder-embedded.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, mst@redhat.com, leiyang@redhat.com, Eugenio =?iso-8859-1?Q?P=E9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , "open list:VIRTIO CORE AND NET DRIVERS" , open list Subject: Re: [PATCH net-next v5 3/4] virtio-net: Map NAPIs to queues Message-ID: Mail-Followup-To: Joe Damato , Jakub Kicinski , netdev@vger.kernel.org, mkarsten@uwaterloo.ca, gerhard@engleder-embedded.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, mst@redhat.com, leiyang@redhat.com, Eugenio =?iso-8859-1?Q?P=E9rez?= , Andrew Lunn , "David S. Miller" , Eric Dumazet , Paolo Abeni , "open list:VIRTIO CORE AND NET DRIVERS" , open list References: <20250227185017.206785-1-jdamato@fastly.com> <20250227185017.206785-4-jdamato@fastly.com> <20250228182759.74de5bec@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Mar 03, 2025 at 12:00:10PM -0500, Joe Damato wrote: > On Mon, Mar 03, 2025 at 11:46:10AM -0500, Joe Damato wrote: > > On Fri, Feb 28, 2025 at 06:27:59PM -0800, Jakub Kicinski wrote: > > > On Thu, 27 Feb 2025 18:50:13 +0000 Joe Damato wrote: > > > > @@ -2870,9 +2883,15 @@ static void refill_work(struct work_struct *work) > > > > for (i = 0; i < vi->curr_queue_pairs; i++) { > > > > struct receive_queue *rq = &vi->rq[i]; > > > > > > > > + rtnl_lock(); > > > > virtnet_napi_disable(rq); > > > > + rtnl_unlock(); > > > > + > > > > still_empty = !try_fill_recv(vi, rq, GFP_KERNEL); > > > > + > > > > + rtnl_lock(); > > > > virtnet_napi_enable(rq); > > > > + rtnl_unlock(); > > > > > > Looks to me like refill_work is cancelled _sync while holding rtnl_lock > > > from the close path. I think this could deadlock? > > > > Good catch, thank you! > > > > It looks like this is also the case in the failure path on > > virtnet_open. > > > > Jason: do you have any suggestions? > > > > It looks like in both open and close disable_delayed_refill is > > called first, before the cancel_delayed_work_sync. > > > > Would something like this solve the problem? > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 76dcd65ec0f2..457115300f05 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -2880,6 +2880,13 @@ static void refill_work(struct work_struct *work) > > bool still_empty; > > int i; > > > > + spin_lock(&vi->refill_lock); > > + if (!vi->refill_enabled) { > > + spin_unlock(&vi->refill_lock); > > + return; > > + } > > + spin_unlock(&vi->refill_lock); > > + > > for (i = 0; i < vi->curr_queue_pairs; i++) { > > struct receive_queue *rq = &vi->rq[i]; > > > > Err, I suppose this also doesn't work because: > > CPU0 CPU1 > rtnl_lock (before CPU0 calls disable_delayed_refill) > virtnet_close refill_work > rtnl_lock() > cancel_sync <= deadlock > > Need to give this a bit more thought. How about we don't use the API at all from refill_work? Patch 4 adds consistent NAPI config state and refill_work isn't a queue resize maybe we don't need to call the netif_queue_set_napi at all since the NAPI IDs are persisted in the NAPI config state and refill_work shouldn't change that? In which case, we could go back to what refill_work was doing before and avoid the problem entirely. What do you think ? diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index 76dcd65ec0f2..d6c8fe670005 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -2883,15 +2883,9 @@ static void refill_work(struct work_struct *work) for (i = 0; i < vi->curr_queue_pairs; i++) { struct receive_queue *rq = &vi->rq[i]; - rtnl_lock(); - virtnet_napi_disable(rq); - rtnl_unlock(); - + napi_disable(&rq->napi); still_empty = !try_fill_recv(vi, rq, GFP_KERNEL); - - rtnl_lock(); - virtnet_napi_enable(rq); - rtnl_unlock(); + virtnet_napi_do_enable(rq->vq, &rq->napi); /* In theory, this can happen: if we don't get any buffers in * we will *never* try to fill again.