netdev - Re: [RFC PATCH net-next 8/9] net: delay device_del until run

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Message-ID: <20210928170229.4c1431c7@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 28 Sep 2021 17:02:29 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Antoine Tenart <atenart@...nel.org>
Cc:     davem@...emloft.net, pabeni@...hat.com, gregkh@...uxfoundation.org,
        ebiederm@...ssion.com, stephen@...workplumber.org,
        herbert@...dor.apana.org.au, juri.lelli@...hat.com,
        netdev@...r.kernel.org
Subject: Re: [RFC PATCH net-next 8/9] net: delay device_del until run_todo

On Tue, 28 Sep 2021 14:54:59 +0200 Antoine Tenart wrote:
> The sysfs removal is done in device_del, and moving it outside of the
> rtnl lock does fix the initial deadlock. With that the trylock/restart
> logic can be removed in a following-up patch.

> diff --git a/net/core/dev.c b/net/core/dev.c
> index a1eab120bb50..d774fbec5d63 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -10593,6 +10593,8 @@ void netdev_run_todo(void)
>  			continue;
>  		}
>  
> +		device_del(&dev->dev);
> +
>  		dev->reg_state = NETREG_UNREGISTERED;
>  
>  		netdev_wait_allrefs(dev);
> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
> index 21c3fdeccf20..e754f00c117b 100644
> --- a/net/core/net-sysfs.c
> +++ b/net/core/net-sysfs.c
> @@ -1955,8 +1955,6 @@ void netdev_unregister_kobject(struct net_device *ndev)
>  	remove_queue_kobjects(ndev);
>  
>  	pm_runtime_set_memalloc_noio(dev, false);
> -
> -	device_del(dev);
>  }
>  
>  /* Create sysfs entries for network device. */

Doesn't this mean there may be sysfs files which are accessible 
for an unregistered netdevice? Isn't the point of having device_del()
under rtnl_lock() to make sure we sysfs handlers can't run on dead
devices?