linux-kernel - Re: [PATCH] fb: Rework locking to fix lock ordering on takeover

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Message-ID: <CAM_iQpWLgnxQR+oYD+Dnh9NprR1-QLjXa6T+dtHUs3A-_N2wmQ@mail.gmail.com>
Date:	Wed, 26 Dec 2012 10:41:14 +0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Sasha Levin <levinsasha928@...il.com>
Cc:	Josh Boyer <jwboyer@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Tobias Schandinat <florianSchandinat@....de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] fb: Rework locking to fix lock ordering on takeover

On Wed, Dec 26, 2012 at 12:08 AM, Sasha Levin <levinsasha928@...il.com> wrote:
> On Tue, Dec 18, 2012 at 10:20 AM, Josh Boyer <jwboyer@...il.com> wrote:
>> On Wed, Nov 21, 2012 at 7:53 AM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>>> On Wed, 21 Nov 2012 07:45:45 -0500
>>> Josh Boyer <jwboyer@...il.com> wrote:
>>>
>>>> On Fri, Nov 16, 2012 at 2:27 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>>>> >
>>>> > [The fb maintainer appears to be absent at the moment].
>>>> >
>>>> > This is needed to fix a pile of lockdep splats that now show up because console_lock()
>>>> > is being properly audited. Hugh Dickins and Sasha Levin have tested it and both reports
>>>> > all looks good. This is probably not the whole story - the entire fb layer has locking
>>>> > confusion problems that were previously hidden but it seems to get the ones people hit
>>>> > in testing. This hopefully explains a few of the weird fb hangs that have been floating
>>>> > around forever.
>>>> >
>>>> > From: Alan Cox <alan@...ux.intel.com>
>>>> >
>>>> > Adjust the console layer to allow a take over call where the caller already
>>>> > holds the locks. Make the fb layer lock in order.
>>>> >
>>>> > This s partly a band aid, the fb layer is terminally confused about the
>>>> > locking rules it uses for its notifiers it seems.
>>>> >
>>>> > Signed-off-by: Alan Cox <alan@...ux.intel.com>
>>>>
>>>> Should this eventually get into the stable trees?
>>>
>>> Thats a question I'm not sure about at this point. I think the bug is
>>> real but not caught by the lock checker in older trees but I've not
>>> investigated.
>>
>> So... this patch seems to still be twisting in the wind.  It should
>> probably be headed into 3.8 at this point, shouldn't it?
>
> Indeed it should. I'm seeing the original warnings in 3.8-rc1 and have
> to carry this patch to avoid them.

This patch can fix the following warning we saw?
http://lkml.org/lkml/2012/12/22/53

I will give it a try.
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