linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000040

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Date:	Sat, 15 Jun 2013 19:43:10 +0300
From:	nirinA raseliarison <nirina.raseliarison@...il.com>
To:	"Guenter Roeck" <linux@...ck-us.net>,
	"Ming Lei" <ming.lei@...onical.com>
Cc:	"nirinA raseliarison" <nirina.raseliarison@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Francois Romieu" <romieu@...zoreil.com>, nic_swsd@...ltek.com,
	"Hayes Wang" <hayeswang@...ltek.com>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at
 0000000000000040

on Sat, 15 Jun 2013 11:08:47 +0300, Ming Lei <ming.lei@...onical.com>  
wrote:

> On Sat, Jun 15, 2013 at 2:30 PM, Guenter Roeck <linux@...ck-us.net>  
> wrote:
>> On Sat, Jun 15, 2013 at 10:32:14AM +0800, Ming Lei wrote:
>>> On Sat, Jun 15, 2013 at 1:07 AM, nirinA raseliarison
>>> <nirina.raseliarison@...il.com> wrote:
>>>
>>> > patch applied and no longer have the bug message when i
>>> > reboot and wake up the ethernet controller.
>>>
>>> I am wondering if Guenter's patch can fix the race really, but I'd  
>>> like to
>>> see Guenter's explanation on his patch.
>>>
>>> The race should be caused by below:
>>>
>>> - request timeout triggered by internal timer
>>>
>>> - user space aborts the requests before the line in  
>>> _request_firmware_load()
>>>
>>>              fw_priv->buf = NULL
>>>
>>> which is run in timeout path
>>>
>>> - then the abort() called from firmware_loading_store() may use a  
>>> freed fw buf
>>> since the timeout path will free the fw buffer.
>>>
>>> Considered clearing 'fw_priv->buf' in _request_firmware_load()() isn't  
>>> protected
>>> by fw_lock now, so Guenter's patch can't avoid the race entirely.
>>>
>> I agree; my patch only protects one specific path, and was based on the
>> observation that access to fw_priv->buf is protected elsewhwere in the  
>> code.
>> My suspicion was that fw_priv->buf was freed while waiting for the  
>> mutex in
>> firmware_loading_store().
>>
>> Your patch is more comprehensive.
>
> OK, thanks for your reply.
>
> I will post out one version for merge, and this one moves the
> "fw_priv->buf = NULL;" into fw_load_abort() for simplifying change.

this is just to let you know that i've tested Ming Lei's latest patch.
thank you very much for the fix and the explanation.

-- 
nirinA
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