linux-kernel - Re: [PATCH] driver core: fix shutdown races with probe/remove(v1)

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Date:	Fri, 8 Jun 2012 09:40:29 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ming Lei <ming.lei@...onical.com>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] driver core: fix shutdown races with probe/remove(v1)

On Fri, 8 Jun 2012, Ming Lei wrote:

> Firstly, .shutdown callback may touch a uninitialized hardware
> if dev->driver is set and .probe is not completed.
> 
> Secondly, device_shutdown() may dereference a null pointer to cause
> oops when dev->driver is cleared after it is checked in
> device_shutdown().
> 
> So just hold device lock and its parent lock if it has to fix the
> races.
> 
> Cc: Alan Stern <stern@...land.harvard.edu>
> Cc: stable@...r.kernel.org
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
>  drivers/base/core.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 346be8b..cbc8bd2 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1820,6 +1820,11 @@ void device_shutdown(void)
>  		list_del_init(&dev->kobj.entry);
>  		spin_unlock(&devices_kset->list_lock);
>  
> +		/*hold lock[s] to avoid races with .probe/.release*/
> +		if (dev->parent)
> +			device_lock(dev->parent);
> +		device_lock(dev);

Would you prefer to use device_trylock in a loop?  I guess this comes 
down to which you prefer: a hang during shutdown, or a crash.  :-)

Alan Stern

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