linux-kernel - Re: [PATCH] lan78xx: Protect runtime_auto check by #ifdef CONFIG

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Date:	Sun, 20 Mar 2016 09:35:52 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Woojung Huh <woojung.huh@...rochip.com>,
	Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
	"David S. Miller" <davem@...emloft.net>,
	Guenter Roeck <linux@...ck-us.net>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lan78xx: Protect runtime_auto check by #ifdef CONFIG_PM

On Sun, 2016-03-20 at 11:43 +0100, Geert Uytterhoeven wrote:
> If CONFIG_PM=n:
> 
>     drivers/net/usb/lan78xx.c: In function ‘lan78xx_get_stats64’:
>     drivers/net/usb/lan78xx.c:3274: error: ‘struct dev_pm_info’ has no member named ‘runtime_auto’
> 
> If PM is disabled, the runtime_auto flag is not available, but auto
> suspend is not enabled anyway.  Hence protect the check for runtime_auto
> by #ifdef CONFIG_PM to fix this.
> 
> Fixes: a59f8c5b048dc938 ("lan78xx: add ndo_get_stats64")
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> Alternatively, we can add a dev_pm_runtime_auto_is_enabled() wrapper to
> include/linux/pm.h, which always return false if CONFIG_PM is disabled.
> 
> The only other user in non-core code (drivers/usb/core/sysfs.c) has a
> big #ifdef CONFIG_PM check around all PM-related code.
> 
> Thoughts?
> ---
>  drivers/net/usb/lan78xx.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/usb/lan78xx.c b/drivers/net/usb/lan78xx.c
> index d36d5ebf37f355f2..7b9ac47b2ecf9905 100644
> --- a/drivers/net/usb/lan78xx.c
> +++ b/drivers/net/usb/lan78xx.c
> @@ -3271,7 +3271,9 @@ struct rtnl_link_stats64 *lan78xx_get_stats64(struct net_device *netdev,
>  	 * periodic reading from HW will prevent from entering USB auto suspend.
>  	 * if autosuspend is disabled, read from HW.
>  	 */
> +#ifdef CONFIG_PM
>  	if (!dev->udev->dev.power.runtime_auto)
> +#endif
>  		lan78xx_update_stats(dev);
>  
>  	mutex_lock(&dev->stats.access_lock);

Note that a ndo_get_stat64() handler is not allowed to sleep,
so the mutex_lock() is not wise...

Historically /proc/net/dev handler but also bonding ndo_get_stats() used
RCU or a rwlock or a spinlock.

So a complete fix would need to get rid of this mutex as well.