linux-kernel - Re: [rfc][patch] mm: lockdep page lock

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Message-ID: <20100326031814.GQ19308@shareable.org>
Date:	Fri, 26 Mar 2010 03:18:14 +0000
From:	Jamie Lokier <jamie@...reable.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Nick Piggin <npiggin@...e.de>, Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [rfc][patch] mm: lockdep page lock

Peter Zijlstra wrote:
> On Tue, 2010-03-16 at 13:21 +1100, Nick Piggin wrote:
> > 
> > 
> > Agreed (btw. Peter is there any way to turn lock debugging back on?
> > it's annoying when cpufreq hotplug code or something early breaks and
> > you have to reboot in order to do any testing).
> 
> Not really, the only way to do that is to get the full system back into
> a known (zero) lock state and then fully reset the lockdep state.

How about: Set a variable nr_pending = number of CPUs, run a task on
each CPU which disables interrupts, atomically decrements nr_pending
and then spins waiting for it to become negative (raw, not counted in
lockdep), and whichever one takes it to zero, that task knows there
are no locks held, and can reset the lockdep state.  Then sets it to
-1 to wake everyone.

-- Jamie
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