linux-kernel - Re: [PATCH -mm] workqueue: debug possible lockups in flush

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Message-ID: <20070419070228.GC1782@ff.dom.local>
Date:	Thu, 19 Apr 2007 09:02:28 +0200
From:	Jarek Poplawski <jarkao2@...pl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] workqueue: debug possible lockups in flush_workqueue

On Thu, Apr 19, 2007 at 08:14:16AM +0200, Ingo Molnar wrote:
> 
> * Jarek Poplawski <jarkao2@...pl> wrote:
> 
> > Here is my patch proposal for detecting possible lockups, when 
> > flush_workqueue caller holds a lock (e.g. rtnl_lock) also used in work 
> > functions.
> 
> looks good in principle - did you test it and it caught a bug that wasnt 
> caught before?

Yes, but it was only my own testing bug... (I'm not a good tester, sorry).

> 
> > +#ifdef CONFIG_PROVE_LOCKING
> > +/* Detect possible flush_workqueue() lockup with circular dependency check. */
> > +static struct lockdep_map flush_dep_map = { .name = "flush_dep_map" };
> > +#endif
> 
> > +#ifdef CONFIG_PROVE_LOCKING
> > +		/* lockdep dependency: flush_dep_map (read) before any lock: */
> > +		lock_acquire(&flush_dep_map, 0, 0, 1, 2, _THIS_IP_);
> > +#endif
> 
> i think the #ifdef should only be needed for the .name initialization - 
> both lock_acquire() and lock_release() maps to NOP if PROVE_LOCKING is 
> off.

There is also DEBUG_LOCK_ALLOC without PROVE_LOCKING possibility,
which isn't usable here.

Jarek P.
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