linux-kernel - Re: linux-next oops in __lock_acquire for process_one

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Message-ID: <alpine.LSU.2.00.1205081106160.4071@eggly.anvils>
Date:	Tue, 8 May 2012 11:11:48 -0700 (PDT)
From:	Hugh Dickins <hughd@...gle.com>
To:	Tejun Heo <tj@...nel.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Yong Zhang <yong.zhang0@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: linux-next oops in __lock_acquire for process_one_work

On Tue, 8 May 2012, Tejun Heo wrote:
> On Tue, May 08, 2012 at 03:03:22PM +0200, Peter Zijlstra wrote:
> > I think there's a problem if indeed we do silly things like small copies
> > like Hugh saw (why would gcc ever generate small copies for objects that
> > are naturally aligned and naturally sized?).
> > 
> > Something like the below should fix that problem, but it doesn't explain
> > the observed issue..
> 
> Hmmm.... Hugh, can you please verify whether this patch makes the
> problem go away somehow?

Sure, but I won't start the run until tonight, and it'll then take
a couple of days for us to be sure (sometimes it hit within the
hour, sometimes it would take half a day).

Certainly the principle, cleaning out the cache, looked sound.

> 
> > @@ -1810,7 +1810,7 @@ __acquires(&gcwq->lock)
> >  	 * lock freed" warnings as well as problems when looking into
> >  	 * work->lockdep_map, make a copy and use that here.
> >  	 */
> > -	struct lockdep_map lockdep_map = work->lockdep_map;
> > +	struct lockdep_map lockdep_map = lockdep_copy_map(&work->lockdep_map);
> 
> If this is the correct fix for whatever reason, maybe we want the copy
> interface to be a bit more conventional?  lockdep_copy_map(to, from)?

Please send me the version of patch you'd like to put in
(lest I make it up myself and you don't like the result).

Hugh
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