linux-kernel - Re: [PATCH] Driver core: fix race in __device_release

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Date:	Fri, 16 Nov 2007 12:04:55 -0500
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <greg@...ah.com>,
	USB development list <linux-usb-devel@...ts.sourceforge.net>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Driver core: fix race in __device_release_driver


On Fri, 2007-11-16 at 11:57 -0500, Alan Stern wrote:
> This patch (as1013) was suggested by David Woodhouse; it fixes a race
> in the driver core.  If a device is unregistered at the same time as
> its driver is unloaded, the driver's code pages may be unmapped while
> the remove method is still running.  The calls to get_driver() and
> put_driver() were intended to prevent this, but they don't work if the
> driver's module count has already dropped to 0.
> 
> Instead, the patch keeps the device on the driver's list until after
> the remove method has returned.  This forces the necessary
> synchronization to occur.
> 
> Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> CC: David Woodhouse <dwmw2@...radead.org>

Since we're submitting it rather than just using it to explain the
problem, I suppose I should add:
Signed-off-by: David Woodhouse <dwmw2@...radead.org>

> ---
> 
> This should be considered for 2.6.24.
> 
> 
> Index: usb-2.6/drivers/base/dd.c
> ===================================================================
> --- usb-2.6.orig/drivers/base/dd.c
> +++ usb-2.6/drivers/base/dd.c
> @@ -289,11 +289,10 @@ static void __device_release_driver(stru
>  {
>  	struct device_driver * drv;
>  
> -	drv = get_driver(dev->driver);
> +	drv = dev->driver;
>  	if (drv) {
>  		driver_sysfs_remove(dev);
>  		sysfs_remove_link(&dev->kobj, "driver");
> -		klist_remove(&dev->knode_driver);
>  
>  		if (dev->bus)
>  			blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
> @@ -306,7 +305,7 @@ static void __device_release_driver(stru
>  			drv->remove(dev);
>  		devres_release_all(dev);
>  		dev->driver = NULL;
> -		put_driver(drv);
> +		klist_remove(&dev->knode_driver);
>  	}
>  }
>  
> 
-- 
dwmw2

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