Message-ID: <20251222180931-mutt-send-email-mst@kernel.org>
Date: Mon, 22 Dec 2025 18:11:31 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: Bui Quang Minh <minhquangbui99@...il.com>,
	Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v2] virtio-net: enable all napis before scheduling
 refill work

On Mon, Dec 22, 2025 at 12:58:01PM +0100, Paolo Abeni wrote:
> On 12/21/25 2:42 PM, Michael S. Tsirkin wrote:
> > On Fri, Dec 19, 2025 at 12:03:29PM +0700, Bui Quang Minh wrote:
> >> On 12/17/25 09:58, Jason Wang wrote:
> >>> On Wed, Dec 17, 2025 at 12:23 AM Bui Quang Minh
> >>> <minhquangbui99@...il.com> wrote:
> >>>> I think we can unconditionally schedule the delayed refill after
> >>>> enabling all the RX NAPIs (don't check the boolean schedule_refill
> >>>> anymore) to ensure that we will have refill work. We can still keep the
> >>>> try_fill_recv here to fill the receive buffer earlier in normal case.
> >>>> What do you think?
> >>> Or we can have a reill_pending
> >>
> >> Okay, let me implement this in the next version.
> >>
> >>> but basically I think we need something
> >>> that is much more simple. That is, using a per rq work instead of a
> >>> global one?
> >>
> >> I think we can leave this in a net-next patch later.
> >>
> >> Thanks,
> >> Quang Minh
> > 
> > i am not sure per rq is not simpler than this pile of tricks.
> FWIW, I agree with Michael: the diffstat of the current patch is quite
> scaring, I don't think a per RQ work would be significantly larger, but
> should be significantly simpler to review and maintain.
> 
> I suggest doing directly the per RQ work implementation.
> 
> Thanks!
> 
> Paolo

I mean a stupidly mechanical move of all refill to per RQ is
rather trivial (CB). Compiled only, feel free to reuse.

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0369dda5ed60..4eb90b4e7b0f 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -379,6 +379,15 @@ struct receive_queue {
 	struct xdp_rxq_info xsk_rxq_info;
 
 	struct xdp_buff **xsk_buffs;
+
+	/* Work struct for delayed refilling if we run low on memory. */
+	struct delayed_work refill;
+
+	/* Is delayed refill enabled? */
+	bool refill_enabled;
+
+	/* The lock to synchronize the access to refill_enabled */
+	spinlock_t refill_lock;
 };
 
 #define VIRTIO_NET_RSS_MAX_KEY_SIZE     40
@@ -441,9 +450,6 @@ struct virtnet_info {
 	/* Packet virtio header size */
 	u8 hdr_len;
 
-	/* Work struct for delayed refilling if we run low on memory. */
-	struct delayed_work refill;
-
 	/* UDP tunnel support */
 	bool tx_tnl;
 
@@ -451,12 +457,6 @@ struct virtnet_info {
 
 	bool rx_tnl_csum;
 
-	/* Is delayed refill enabled? */
-	bool refill_enabled;
-
-	/* The lock to synchronize the access to refill_enabled */
-	spinlock_t refill_lock;
-
 	/* Work struct for config space updates */
 	struct work_struct config_work;
 
@@ -720,18 +720,11 @@ static void virtnet_rq_free_buf(struct virtnet_info *vi,
 		put_page(virt_to_head_page(buf));
 }
 
-static void enable_delayed_refill(struct virtnet_info *vi)
+static void disable_delayed_refill(struct receive_queue *rq)
 {
-	spin_lock_bh(&vi->refill_lock);
-	vi->refill_enabled = true;
-	spin_unlock_bh(&vi->refill_lock);
-}
-
-static void disable_delayed_refill(struct virtnet_info *vi)
-{
-	spin_lock_bh(&vi->refill_lock);
-	vi->refill_enabled = false;
-	spin_unlock_bh(&vi->refill_lock);
+	spin_lock_bh(&rq->refill_lock);
+	rq->refill_enabled = false;
+	spin_unlock_bh(&rq->refill_lock);
 }
 
 static void enable_rx_mode_work(struct virtnet_info *vi)
@@ -2935,38 +2928,20 @@ static void virtnet_napi_disable(struct receive_queue *rq)
 
 static void refill_work(struct work_struct *work)
 {
-	struct virtnet_info *vi =
-		container_of(work, struct virtnet_info, refill.work);
+	struct receive_queue *rq = container_of(work, struct receive_queue,
+						refill.work);
+	struct virtnet_info *vi = rq->vq->vdev->priv;
 	bool still_empty;
-	int i;
 
-	for (i = 0; i < vi->curr_queue_pairs; i++) {
-		struct receive_queue *rq = &vi->rq[i];
+	napi_disable(&rq->napi);
+	still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
+	virtnet_napi_do_enable(rq->vq, &rq->napi);
 
-		/*
-		 * When queue API support is added in the future and the call
-		 * below becomes napi_disable_locked, this driver will need to
-		 * be refactored.
-		 *
-		 * One possible solution would be to:
-		 *   - cancel refill_work with cancel_delayed_work (note:
-		 *     non-sync)
-		 *   - cancel refill_work with cancel_delayed_work_sync in
-		 *     virtnet_remove after the netdev is unregistered
-		 *   - wrap all of the work in a lock (perhaps the netdev
-		 *     instance lock)
-		 *   - check netif_running() and return early to avoid a race
-		 */
-		napi_disable(&rq->napi);
-		still_empty = !try_fill_recv(vi, rq, GFP_KERNEL);
-		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.
-		 */
-		if (still_empty)
-			schedule_delayed_work(&vi->refill, HZ/2);
-	}
+	/* In theory, this can happen: if we don't get any buffers in
+	 * we will *never* try to fill again.
+	 */
+	if (still_empty)
+		schedule_delayed_work(&rq->refill, HZ / 2);
 }
 
 static int virtnet_receive_xsk_bufs(struct virtnet_info *vi,
@@ -3033,10 +3008,10 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
 
 	if (rq->vq->num_free > min((unsigned int)budget, virtqueue_get_vring_size(rq->vq)) / 2) {
 		if (!try_fill_recv(vi, rq, GFP_ATOMIC)) {
-			spin_lock(&vi->refill_lock);
-			if (vi->refill_enabled)
-				schedule_delayed_work(&vi->refill, 0);
-			spin_unlock(&vi->refill_lock);
+			spin_lock(&rq->refill_lock);
+			if (rq->refill_enabled)
+				schedule_delayed_work(&rq->refill, 0);
+			spin_unlock(&rq->refill_lock);
 		}
 	}
 
@@ -3216,13 +3191,14 @@ static int virtnet_open(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i, err;
 
-	enable_delayed_refill(vi);
-
 	for (i = 0; i < vi->max_queue_pairs; i++) {
+		/* Enable refill work before enabling NAPI */
+		vi->rq[i].refill_enabled = true;
+
 		if (i < vi->curr_queue_pairs)
 			/* Make sure we have some buffers: if oom use wq. */
 			if (!try_fill_recv(vi, &vi->rq[i], GFP_KERNEL))
-				schedule_delayed_work(&vi->refill, 0);
+				schedule_delayed_work(&vi->rq[i].refill, 0);
 
 		err = virtnet_enable_queue_pair(vi, i);
 		if (err < 0)
@@ -3241,11 +3217,10 @@ static int virtnet_open(struct net_device *dev)
 	return 0;
 
 err_enable_qp:
-	disable_delayed_refill(vi);
-	cancel_delayed_work_sync(&vi->refill);
-
 	for (i--; i >= 0; i--) {
+		disable_delayed_refill(&vi->rq[i]);
 		virtnet_disable_queue_pair(vi, i);
+		cancel_delayed_work_sync(&vi->rq[i].refill);
 		virtnet_cancel_dim(vi, &vi->rq[i].dim);
 	}
 
@@ -3437,29 +3412,19 @@ static void __virtnet_rx_pause(struct virtnet_info *vi,
 	}
 }
 
+static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
+{
+	disable_delayed_refill(rq);
+	cancel_delayed_work_sync(&rq->refill);
+	__virtnet_rx_pause(vi, rq);
+}
+
 static void virtnet_rx_pause_all(struct virtnet_info *vi)
 {
 	int i;
 
-	/*
-	 * Make sure refill_work does not run concurrently to
-	 * avoid napi_disable race which leads to deadlock.
-	 */
-	disable_delayed_refill(vi);
-	cancel_delayed_work_sync(&vi->refill);
 	for (i = 0; i < vi->max_queue_pairs; i++)
-		__virtnet_rx_pause(vi, &vi->rq[i]);
-}
-
-static void virtnet_rx_pause(struct virtnet_info *vi, struct receive_queue *rq)
-{
-	/*
-	 * Make sure refill_work does not run concurrently to
-	 * avoid napi_disable race which leads to deadlock.
-	 */
-	disable_delayed_refill(vi);
-	cancel_delayed_work_sync(&vi->refill);
-	__virtnet_rx_pause(vi, rq);
+		virtnet_rx_pause(vi, &vi->rq[i]);
 }
 
 static void __virtnet_rx_resume(struct virtnet_info *vi,
@@ -3474,15 +3439,17 @@ static void __virtnet_rx_resume(struct virtnet_info *vi,
 	if (running)
 		virtnet_napi_enable(rq);
 
+	spin_lock_bh(&rq->refill_lock);
+	rq->refill_enabled = true;
 	if (schedule_refill)
-		schedule_delayed_work(&vi->refill, 0);
+		schedule_delayed_work(&rq->refill, 0);
+	spin_unlock_bh(&rq->refill_lock);
 }
 
 static void virtnet_rx_resume_all(struct virtnet_info *vi)
 {
 	int i;
 
-	enable_delayed_refill(vi);
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		if (i < vi->curr_queue_pairs)
 			__virtnet_rx_resume(vi, &vi->rq[i], true);
@@ -3493,7 +3460,6 @@ static void virtnet_rx_resume_all(struct virtnet_info *vi)
 
 static void virtnet_rx_resume(struct virtnet_info *vi, struct receive_queue *rq)
 {
-	enable_delayed_refill(vi);
 	__virtnet_rx_resume(vi, rq, true);
 }
 
@@ -3768,6 +3734,7 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
 	struct virtio_net_rss_config_trailer old_rss_trailer;
 	struct net_device *dev = vi->dev;
 	struct scatterlist sg;
+	int i;
 
 	if (!vi->has_cvq || !virtio_has_feature(vi->vdev, VIRTIO_NET_F_MQ))
 		return 0;
@@ -3821,10 +3788,14 @@ 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. */
-	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);
+	if (dev->flags & IFF_UP) {
+		for (i = 0; i < vi->curr_queue_pairs; i++) {
+			spin_lock_bh(&vi->rq[i].refill_lock);
+			if (vi->rq[i].refill_enabled)
+				schedule_delayed_work(&vi->rq[i].refill, 0);
+			spin_unlock_bh(&vi->rq[i].refill_lock);
+		}
+	}
 
 	return 0;
 }
@@ -3834,10 +3805,6 @@ static int virtnet_close(struct net_device *dev)
 	struct virtnet_info *vi = netdev_priv(dev);
 	int i;
 
-	/* Make sure NAPI doesn't schedule refill work */
-	disable_delayed_refill(vi);
-	/* Make sure refill_work doesn't re-enable napi! */
-	cancel_delayed_work_sync(&vi->refill);
 	/* Prevent the config change callback from changing carrier
 	 * after close
 	 */
@@ -3848,7 +3815,9 @@ static int virtnet_close(struct net_device *dev)
 	cancel_work_sync(&vi->config_work);
 
 	for (i = 0; i < vi->max_queue_pairs; i++) {
+		disable_delayed_refill(&vi->rq[i]);
 		virtnet_disable_queue_pair(vi, i);
+		cancel_delayed_work_sync(&vi->rq[i].refill);
 		virtnet_cancel_dim(vi, &vi->rq[i].dim);
 	}
 
@@ -5793,7 +5762,6 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
-	enable_delayed_refill(vi);
 	enable_rx_mode_work(vi);
 
 	if (netif_running(vi->dev)) {
@@ -6550,7 +6518,6 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 	if (!vi->rq)
 		goto err_rq;
 
-	INIT_DELAYED_WORK(&vi->refill, refill_work);
 	for (i = 0; i < vi->max_queue_pairs; i++) {
 		vi->rq[i].pages = NULL;
 		netif_napi_add_config(vi->dev, &vi->rq[i].napi, virtnet_poll,
@@ -6567,6 +6534,8 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 		u64_stats_init(&vi->rq[i].stats.syncp);
 		u64_stats_init(&vi->sq[i].stats.syncp);
 		mutex_init(&vi->rq[i].dim_lock);
+		INIT_DELAYED_WORK(&vi->rq[i].refill, refill_work);
+		spin_lock_init(&vi->rq[i].refill_lock);
 	}
 
 	return 0;
@@ -6892,7 +6861,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 	INIT_WORK(&vi->config_work, virtnet_config_changed_work);
 	INIT_WORK(&vi->rx_mode_work, virtnet_rx_mode_work);
-	spin_lock_init(&vi->refill_lock);
 
 	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF)) {
 		vi->mergeable_rx_bufs = true;
@@ -7156,7 +7124,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	net_failover_destroy(vi->failover);
 free_vqs:
 	virtio_reset_device(vdev);
-	cancel_delayed_work_sync(&vi->refill);
+	for (i = 0; i < vi->max_queue_pairs; i++)
+		cancel_delayed_work_sync(&vi->rq[i].refill);
 	free_receive_page_frags(vi);
 	virtnet_del_vqs(vi);
 free:

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