linux-kernel - Re: BUG: circular locking dependency detected

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Date:	Thu, 31 Jan 2013 10:04:05 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Russell King <rmk@....linux.org.uk>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: BUG: circular locking dependency detected

On Thu, Jan 31, 2013 at 9:52 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Thu, Jan 31, 2013 at 9:19 AM, Russell King <rmk@....linux.org.uk> wrote:
>>
>> So... what you seem to be telling me is that 3.9 is going to be a
>> release which issues lockdep complaints when the console blanks, and
>> you think that's acceptable?
>>
>> Adding Linus and Andrew so they're aware of this issue...
>
> Oh, we're extremely aware of it. And it's not a new issue, the locking
> problem have apparently been around forever, although I'm not sure why
> the lockdep splat itself started happening only recently.
>
> They'll make it into 3.9, it's 3.8 that won't have them. The patches
> initially caused way *worse* behavior than just a lockdep splat - they
> caused actual hard lockups (and that was *after* the initial series of
> fixes). That got fixed (hopefully for the last case!) fairly recently,
> and I'm not willing to take the scary patch-series that has had
> several problem cases.

Well we didn't have any lock validation support before Daniel added it
a couple of kernels back,
so instead of hidden locking problems we've had from time began, we now have
lockdep detectable locking problems.

Dave.
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