Message-ID: <aRNsHUjW3PybGXCK@horms.kernel.org>
Date: Tue, 11 Nov 2025 17:02:21 +0000
From: Simon Horman <horms@...nel.org>
To: Dipayaan Roy <dipayanroy@...ux.microsoft.com>
Cc: kys@...rosoft.com, haiyangz@...rosoft.com, wei.liu@...nel.org,
	decui@...rosoft.com, andrew+netdev@...n.ch, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	longli@...rosoft.com, kotaranov@...rosoft.com,
	shradhagupta@...ux.microsoft.com, ssengar@...ux.microsoft.com,
	ernis@...ux.microsoft.com, shirazsaleem@...rosoft.com,
	linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	dipayanroy@...rosoft.com
Subject: Re: [PATCH net-next, v3] net: mana: Implement ndo_tx_timeout and
 serialize queue resets per port.

On Mon, Nov 10, 2025 at 02:35:41AM -0800, Dipayaan Roy wrote:
> Implement .ndo_tx_timeout for MANA so any stalled TX queue can be detected
> and a device-controlled port reset for all queues can be scheduled to a
> ordered workqueue. The reset for all queues on stall detection is
> recomended by hardware team.
> 
> The change introduces a single ordered workqueue
> ("mana_per_port_queue_reset_wq") with WQ_UNBOUND | WQ_MEM_RECLAIM and
> queues exactly one work_struct per port onto it.

I see that this goes some way to addressing Jakub's feedback
on the commit message in his review of v2. But I this paragraph
isn't adding much in it's current form. It seems to me some
explanation of why why WQ_UNBOUND and WQ_MEM_RECLAIM are used is
appropriate.

[1] https://lore.kernel.org/all/20251029182233.59aea2d3@kernel.org/

> Reviewed-by: Pavan Chebbi <pavan.chebbi@...adcom.com>
> Reviewed-by: Haiyang Zhang <haiyangz@...rosoft.com>
> Signed-off-by: Dipayaan Roy <dipayanroy@...ux.microsoft.com>
> ---
> Changes in v3:
>   -Fixed commit meesage, removed rtnl_trylock and added
>    disable_work_sync, fixed mana_queue_reset_work, and few
>    cosmetics.
> Changes in v2:
>   -Fixed cosmetic changes.
> ---
> ---
>  drivers/net/ethernet/microsoft/mana/mana_en.c | 78 ++++++++++++++++++-
>  include/net/mana/gdma.h                       |  7 +-
>  include/net/mana/mana.h                       |  7 ++
>  3 files changed, 90 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> index cccd5b63cee6..636df3b066c5 100644
> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> @@ -298,6 +298,42 @@ static int mana_get_gso_hs(struct sk_buff *skb)
>  	return gso_hs;
>  }
>  
> +static void mana_per_port_queue_reset_work_handler(struct work_struct *work)
> +{
> +	struct mana_queue_reset_work *reset_queue_work =
> +			container_of(work, struct mana_queue_reset_work, work);
> +
> +	struct mana_port_context *apc = container_of(reset_queue_work,
> +						     struct mana_port_context,
> +						     queue_reset_work);
> +	struct net_device *ndev = apc->ndev;
> +	int err;
> +
> +	rtnl_lock();
> +
> +	/* Pre-allocate buffers to prevent failure in mana_attach later */
> +	err = mana_pre_alloc_rxbufs(apc, ndev->mtu, apc->num_queues);
> +	if (err) {
> +		netdev_err(ndev, "Insufficient memory for reset post tx stall detection\n");
> +		goto out;
> +	}
> +
> +	err = mana_detach(ndev, false);
> +	if (err) {
> +		netdev_err(ndev, "mana_detach failed: %d\n", err);
> +		goto dealloc_pre_rxbufs;
> +	}
> +
> +	err = mana_attach(ndev);
> +	if (err)
> +		netdev_err(ndev, "mana_attach failed: %d\n", err);
> +
> +dealloc_pre_rxbufs:
> +	mana_pre_dealloc_rxbufs(apc);
> +out:
> +	rtnl_unlock();
> +}
> +
>  netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  {
>  	enum mana_tx_pkt_format pkt_fmt = MANA_SHORT_PKT_FMT;
> @@ -802,6 +838,23 @@ static int mana_change_mtu(struct net_device *ndev, int new_mtu)
>  	return err;
>  }
>  
> +static void mana_tx_timeout(struct net_device *netdev, unsigned int txqueue)
> +{
> +	struct mana_port_context *apc = netdev_priv(netdev);
> +	struct mana_context *ac = apc->ac;
> +	struct gdma_context *gc = ac->gdma_dev->gdma_context;
> +
> +	/* Already in service, hence tx queue reset is not required.*/
> +	if (gc->in_service)
> +		return;
> +
> +	/* Note: If there are pending queue reset work for this port(apc),
> +	 * subsequent request queued up from here are ignored. This is because
> +	 * we are using the same work instance per port(apc).
> +	 */
> +	queue_work(ac->per_port_queue_reset_wq, &apc->queue_reset_work.work);
> +}
> +
>  static int mana_shaper_set(struct net_shaper_binding *binding,
>  			   const struct net_shaper *shaper,
>  			   struct netlink_ext_ack *extack)
> @@ -884,7 +937,9 @@ static const struct net_device_ops mana_devops = {
>  	.ndo_bpf		= mana_bpf,
>  	.ndo_xdp_xmit		= mana_xdp_xmit,
>  	.ndo_change_mtu		= mana_change_mtu,
> -	.net_shaper_ops         = &mana_shaper_ops,
> +	.ndo_tx_timeout		= mana_tx_timeout,
> +	.net_shaper_ops		= &mana_shaper_ops,
> +
>  };
>  
>  static void mana_cleanup_port_context(struct mana_port_context *apc)
> @@ -3244,6 +3299,7 @@ static int mana_probe_port(struct mana_context *ac, int port_idx,
>  	ndev->min_mtu = ETH_MIN_MTU;
>  	ndev->needed_headroom = MANA_HEADROOM;
>  	ndev->dev_port = port_idx;
> +	ndev->watchdog_timeo = 15 * HZ;
>  	SET_NETDEV_DEV(ndev, gc->dev);
>  
>  	netif_set_tso_max_size(ndev, GSO_MAX_SIZE);
> @@ -3283,6 +3339,10 @@ static int mana_probe_port(struct mana_context *ac, int port_idx,
>  
>  	debugfs_create_u32("current_speed", 0400, apc->mana_port_debugfs, &apc->speed);
>  
> +	/* Initialize the per port queue reset work.*/
> +	INIT_WORK(&apc->queue_reset_work.work,
> +		  mana_per_port_queue_reset_work_handler);
> +

I think it would make more sense to move this to before the call to
register_netdev(), which is a few lines above this hunk.

I suppose that because a watchdog timeout is involved, it won't happen in
practice, but in theory could fire ndo_tx_timeout before INIT_WORK is
called, resulting in access to the work queue before it is initialised.

>  	return 0;
>  
>  free_indir:
> @@ -3488,6 +3548,15 @@ int mana_probe(struct gdma_dev *gd, bool resuming)
>  	if (ac->num_ports > MAX_PORTS_IN_MANA_DEV)
>  		ac->num_ports = MAX_PORTS_IN_MANA_DEV;
>  
> +	ac->per_port_queue_reset_wq =
> +			alloc_ordered_workqueue("mana_per_port_queue_reset_wq",
> +						WQ_UNBOUND | WQ_MEM_RECLAIM);
> +	if (!ac->per_port_queue_reset_wq) {
> +		dev_err(dev, "Failed to allocate per port queue reset workqueue\n");
> +		err = -ENOMEM;
> +		goto out;
> +	}
> +
>  	if (!resuming) {
>  		for (i = 0; i < ac->num_ports; i++) {
>  			err = mana_probe_port(ac, i, &ac->ports[i]);

It is not strictly related to this patch, but the lines above the hunk
below look like this:

		apc = netdev_priv(ndev);
		if (!ndev) {
			if (i == 0)
				dev_err(dev, "No net device to remove\n");

If ndev is null then the call to netdev_priv() will result in a
NULL pointer dereference. So I think it should be moved
to after the check for !ndev.

> @@ -3557,6 +3626,8 @@ void mana_remove(struct gdma_dev *gd, bool suspending)
>  			goto out;
>  		}
>  
> +		disable_work_sync(&apc->queue_reset_work.work);
> +
>  		/* All cleanup actions should stay after rtnl_lock(), otherwise
>  		 * other functions may access partially cleaned up data.
>  		 */

Comments on code flagged by Claude Code with
https://github.com/masoncl/review-prompts/

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