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

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Message-ID: <20250801110518.GN8494@horms.kernel.org>
Date: Fri, 1 Aug 2025 12:05:18 +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 Fri, Aug 01, 2025 at 06:44:36PM +0800, Jijie Shao wrote:
> 
> on 2025/8/1 18:05, Simon Horman wrote:
> > 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.
> 
> Yes, just like the following, it can lead to reset and net open concurrency.
> ===========
> 
>      reset1                                              reset2                               open
> 
> set_bit HBG_NIC_STATE_RESETTING
> 
>      netif_device_detach()
>      resetting...
> 
> clear_bit HBG_NIC_STATE_RESETTING
>                                               set_bit HBG_NIC_STATE_RESETTING
>                                                    netif_device_detach()
> 
>       netif_device_attach()
>                                                          resetting...                     hbg_net_open()
>                                                                                           hbg_txrx_init()
> 
>                                               clear_bit HBG_NIC_STATE_RESETTING
>                                                       netif_device_attach()
> 
> ============
> Thank you for your reminder.
> I will fix it in V2

Likewise, thanks.

-- 
pw-bot: cr