netdev - Re: [PATCH iwl-net] igc: Fix deadlock on module removal

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Date: Sun, 14 Apr 2024 11:02:06 +0200
From: Lukas Wunner <lukas@...ner.de>
To: Kurt Kanzenbach <kurt@...utronix.de>,
	Roman Lozko <lozko.roma@...il.com>
Cc: Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew@...n.ch>, Sasha Neftin <sasha.neftin@...el.com>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org
Subject: Re: [PATCH iwl-net] igc: Fix deadlock on module removal

[cc += Roman Lozko who originally reported the issue]

On Sun, Apr 14, 2024 at 09:44:10AM +0200, Kurt Kanzenbach wrote:
> unregister_netdev() acquires the RNTL lock and releases the LEDs bound
> to that netdevice. However, netdev_trig_deactivate() and later
> unregister_netdevice_notifier() try to acquire the RTNL lock again.
> 
> Avoid this situation by not using the device-managed LED class
> functions.
> 
> Suggested-by: Lukas Wunner <lukas@...ner.de>
> Fixes: ea578703b03d ("igc: Add support for LEDs on i225/i226")
> Signed-off-by: Kurt Kanzenbach <kurt@...utronix.de>

This patch is almost a 1:1 copy of the patch I submitted on April 5:

https://lore.kernel.org/all/ZhBN9p1yOyciXkzw@wunner.de/

I think it is mandatory that you include a Signed-off-by with my name
in that case.  Arguably the commit author ("From:") should also be me.

Moreover this is missing a Reported-by tag with Roman Lozko's name.

AFAICS the only changes that you made are:
- rename igc_led_teardown() to igc_led_free()
- rename ret to err
- replace devm_kcalloc() with kcalloc()
  (and you introduced a memory leak while doing so, see below)

Honestly I don't see how those small changes justify omitting a
Signed-off-by or assuming authorship.

I would have been happy to submit a patch myself, I was waiting
for a Tested-by from Roman or you.


> --- a/drivers/net/ethernet/intel/igc/igc.h
> +++ b/drivers/net/ethernet/intel/igc/igc.h
> @@ -164,6 +164,8 @@ struct igc_ring {
>  	struct xsk_buff_pool *xsk_pool;
>  } ____cacheline_internodealigned_in_smp;
>  
> +struct igc_led_classdev;

Unnecessary forward declaration, this compiled fine for me without it.


>  int igc_led_setup(struct igc_adapter *adapter)
>  {
>  	struct net_device *netdev = adapter->netdev;
> -	struct device *dev = &netdev->dev;
>  	struct igc_led_classdev *leds;
> -	int i;
> +	int i, err;
>  
>  	mutex_init(&adapter->led_mutex);
>  
> -	leds = devm_kcalloc(dev, IGC_NUM_LEDS, sizeof(*leds), GFP_KERNEL);
> +	leds = kcalloc(IGC_NUM_LEDS, sizeof(*leds), GFP_KERNEL);
>  	if (!leds)
>  		return -ENOMEM;
>  
> -	for (i = 0; i < IGC_NUM_LEDS; i++)
> -		igc_setup_ldev(leds + i, netdev, i);
> +	for (i = 0; i < IGC_NUM_LEDS; i++) {
> +		err = igc_setup_ldev(leds + i, netdev, i);
> +		if (err)
> +			goto err;
> +	}
> +
> +	adapter->leds = leds;
>  
>  	return 0;
> +
> +err:
> +	for (i--; i >= 0; i--)
> +		led_classdev_unregister(&((leds + i)->led));
> +
> +	return err;
> +}

"leds" allocation is leaked in the error path.

This memory leak was not present in my original patch.  Not good!

Thanks,

Lukas