linux-kernel - Re: [tip:sched/urgent] lockdep: Fix lock_is

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Message-ID: <20110607180638.GB22523@elte.hu>
Date:	Tue, 7 Jun 2011 20:06:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	lists@...-jansens.de, mingo@...hat.com, hpa@...or.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	stable@...nel.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/urgent] lockdep: Fix lock_is_held() on recursion


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Tue, 2011-06-07 at 12:02 +0000, tip-bot for Peter Zijlstra wrote:
> > Commit-ID:  f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d
> > Gitweb:     http://git.kernel.org/tip/f2513cde93f0957d5dc6c09bc24b0cccd27d8e1d
> > Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > AuthorDate: Mon, 6 Jun 2011 12:32:43 +0200
> > Committer:  Ingo Molnar <mingo@...e.hu>
> > CommitDate: Tue, 7 Jun 2011 12:25:50 +0200
> > 
> > lockdep: Fix lock_is_held() on recursion
> > 
> > The main lock_is_held() user is lockdep_assert_held(), avoid false
> > assertions in lockdep_off() sections by unconditionally reporting the
> > lock is taken.
> > 
> > [ the reason this is important is a lockdep_assert_held() in ttwu()
> >   which triggers a warning under lockdep_off() as in printk() which
> >   can trigger another wakeup and lock up due to spinlock
> >   recursion, as reported and heroically debugged by Arne Jansen ]
> > 
> > Reported-and-tested-by: Arne Jansen <lists@...-jansens.de>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: <stable@...nel.org>
> 
> Not _that_ critical for stable since the offending lockdep_assert_held()
> doesn't exist in .39, still definitely won't hurt.

Correct, the bug was hard enough to find, i didnt want someone else 
to trigger a similar one. There's numerous lockdep_assert_held() 
instances all around the tree.

Thanks,

	Ingo
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