linux-kernel - Re: Possible deadlock when suspending framebuffer

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Message-ID: <4DF7B0B4.4060002@gmx.de>
Date:	Tue, 14 Jun 2011 19:04:20 +0000
From:	Florian Tobias Schandinat <FlorianSchandinat@....de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Paul Mundt <lethal@...ux-sh.org>, linux-fbdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Francis Moreau <francis.moro@...il.com>
Subject: Re: Possible deadlock when suspending framebuffer

Hi Linus,

On 06/14/2011 06:15 PM, Linus Torvalds wrote:
> Paul, fbdev people.. Comments? This was sent to me and lkml, the right
> people probably didn't see it.

Sounds very familiar. Indeed a quick glance at my archive revealed 2 
approaches/patches dealing with similar issues
http://marc.info/?l=linux-fbdev&m=129539210207429&w=2
http://marc.info/?l=linux-fbdev&m=129700789632450&w=2

I did not have time to verify that those do actually get those things right 
everywhere but the first one looks good and should also solve this issue I think.


Regards,

Florian Tobias Schandinat

>
> I doubt it's a big problem in practice, but..
>
>                        Linus
>
> On Tue, Jun 14, 2011 at 6:10 AM, Francis Moreau<francis.moro@...il.com>  wrote:
>> Hello,
>>
>> I noticed that a possible deadlock can happen when the current frame
>> buffering is being suspended and a new frambuffer device is being
>> registred at the same time.
>>
>> When suspending the current frambuffer by doing : echo 1
>>> /sys/class/graphics/fb0/state, the kernel actually takes the
>> following locks in that order: console_lock, lock_fb_info (see
>> store_fbstate()).
>>
>> However when a new framebuffer is coming in, the lock sequence is:
>> lock_fb_info (taken by do_remove_conflicting_framebuffer()),
>> console_lock() (taken by unbind_console).
>>
>> I don't know how this should be fixed though...
>>
>> Thanks
>> --
>> Francis
>>
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