linux-kernel - Re: [PATCH net 1/3] net: hibmcge: fix rtnl deadlock issue

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Message-ID: <20250801100520.GJ8494@horms.kernel.org>
Date: Fri, 1 Aug 2025 11:05:20 +0100
From: Simon Horman <horms@...nel.org>
To: Jijie Shao <shaojijie@...wei.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, andrew+netdev@...n.ch, shenjian15@...wei.com,
	liuyonglong@...wei.com, chenhao418@...wei.com,
	jonathan.cameron@...wei.com, shameerali.kolothum.thodi@...wei.com,
	salil.mehta@...wei.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/3] net: hibmcge: fix rtnl deadlock issue

On Thu, Jul 31, 2025 at 09:47:47PM +0800, Jijie Shao wrote:
> Currently, the hibmcge netdev acquires the rtnl_lock in
> pci_error_handlers.reset_prepare() and releases it in
> pci_error_handlers.reset_done().
> 
> However, in the PCI framework:
> pci_reset_bus - __pci_reset_slot - pci_slot_save_and_disable_locked -
>  pci_dev_save_and_disable - err_handler->reset_prepare(dev);
> 
> In pci_slot_save_and_disable_locked():
> 	list_for_each_entry(dev, &slot->bus->devices, bus_list) {
> 		if (!dev->slot || dev->slot!= slot)
> 			continue;
> 		pci_dev_save_and_disable(dev);
> 		if (dev->subordinate)
> 			pci_bus_save_and_disable_locked(dev->subordinate);
> 	}
> 
> This will iterate through all devices under the current bus and execute
> err_handler->reset_prepare(), causing two devices of the hibmcge driver
> to sequentially request the rtnl_lock, leading to a deadlock.
> 
> Since the driver now executes netif_device_detach()
> before the reset process, it will not concurrently with
> other netdev APIs, so there is no need to hold the rtnl_lock now.
> 
> Therefore, this patch removes the rtnl_lock during the reset process and
> adjusts the position of HBG_NIC_STATE_RESETTING to ensure
> that multiple resets are not executed concurrently.
> 
> Fixes: 3f5a61f6d504f ("net: hibmcge: Add reset supported in this module")
> Signed-off-by: Jijie Shao <shaojijie@...wei.com>
> ---
>  drivers/net/ethernet/hisilicon/hibmcge/hbg_err.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/hisilicon/hibmcge/hbg_err.c b/drivers/net/ethernet/hisilicon/hibmcge/hbg_err.c
> index 503cfbfb4a8a..94bc6f0da912 100644
> --- a/drivers/net/ethernet/hisilicon/hibmcge/hbg_err.c
> +++ b/drivers/net/ethernet/hisilicon/hibmcge/hbg_err.c
> @@ -53,9 +53,11 @@ static int hbg_reset_prepare(struct hbg_priv *priv, enum hbg_reset_type type)
>  {
>  	int ret;
>  
> -	ASSERT_RTNL();
> +	if (test_and_set_bit(HBG_NIC_STATE_RESETTING, &priv->state))
> +		return -EBUSY;
>  
>  	if (netif_running(priv->netdev)) {
> +		clear_bit(HBG_NIC_STATE_RESETTING, &priv->state);
>  		dev_warn(&priv->pdev->dev,
>  			 "failed to reset because port is up\n");
>  		return -EBUSY;
> @@ -64,7 +66,6 @@ static int hbg_reset_prepare(struct hbg_priv *priv, enum hbg_reset_type type)
>  	netif_device_detach(priv->netdev);
>  
>  	priv->reset_type = type;
> -	set_bit(HBG_NIC_STATE_RESETTING, &priv->state);
>  	clear_bit(HBG_NIC_STATE_RESET_FAIL, &priv->state);
>  	ret = hbg_hw_event_notify(priv, HBG_HW_EVENT_RESET);
>  	if (ret) {
> @@ -84,10 +85,8 @@ static int hbg_reset_done(struct hbg_priv *priv, enum hbg_reset_type type)
>  	    type != priv->reset_type)
>  		return 0;
>  
> -	ASSERT_RTNL();
> -
> -	clear_bit(HBG_NIC_STATE_RESETTING, &priv->state);
>  	ret = hbg_rebuild(priv);
> +	clear_bit(HBG_NIC_STATE_RESETTING, &priv->state);

Hi Jijie,

If I understand things correctly, then with this patch the
HBG_NIC_STATE_RESETTING bit is used to prevent concurrent execution.

Noting that a reset may be triggered via eththool, where hbg_reset() is
used as a callback, I am concerned about concurrency implications for lines
below this one.

>  	if (ret) {
>  		priv->stats.reset_fail_cnt++;
>  		set_bit(HBG_NIC_STATE_RESET_FAIL, &priv->state);
> @@ -101,12 +100,10 @@ static int hbg_reset_done(struct hbg_priv *priv, enum hbg_reset_type type)
>  	return ret;
>  }
>  
> -/* must be protected by rtnl lock */
>  int hbg_reset(struct hbg_priv *priv)
>  {
>  	int ret;
>  
> -	ASSERT_RTNL();
>  	ret = hbg_reset_prepare(priv, HBG_RESET_TYPE_FUNCTION);
>  	if (ret)
>  		return ret;
> @@ -171,7 +168,6 @@ static void hbg_pci_err_reset_prepare(struct pci_dev *pdev)
>  	struct net_device *netdev = pci_get_drvdata(pdev);
>  	struct hbg_priv *priv = netdev_priv(netdev);
>  
> -	rtnl_lock();
>  	hbg_reset_prepare(priv, HBG_RESET_TYPE_FLR);
>  }
>  
> @@ -181,7 +177,6 @@ static void hbg_pci_err_reset_done(struct pci_dev *pdev)
>  	struct hbg_priv *priv = netdev_priv(netdev);
>  
>  	hbg_reset_done(priv, HBG_RESET_TYPE_FLR);
> -	rtnl_unlock();
>  }
>  
>  static const struct pci_error_handlers hbg_pci_err_handler = {
> -- 
> 2.33.0
>