linux-kernel - Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature

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Date:   Thu, 17 Aug 2017 16:04:04 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Byungchul Park <byungchul.park@....com>,
        Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org,
        walken@...gle.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, willy@...radead.org, npiggin@...il.com,
        kernel-team@....com
Subject: Re: [PATCH v8 00/14] lockdep: Implement crossrelease feature

On Thu, Aug 17, 2017 at 09:48:11AM +0200, Ingo Molnar wrote:
> 
> * Boqun Feng <boqun.feng@...il.com> wrote:
> 
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -2431,6 +2431,27 @@ struct wq_barrier {
> >  	struct task_struct	*task;	/* purely informational */
> >  };
> >  
> > +#ifdef CONFIG_LOCKDEP_COMPLETE
> > +# define INIT_WQ_BARRIER_ONSTACK(barr, func, target)				\
> > +do {										\
> > +	INIT_WORK_ONSTACK(&(barr)->work, func);					\
> > +	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&(barr)->work));	\
> > +	lockdep_init_map_crosslock((struct lockdep_map *)&(barr)->done.map,	\
> > +				   "(complete)" #barr,				\
> > +				   (target)->lockdep_map.key, 1); 		\
> > +	__init_completion(&barr->done);						\
> > +	barr->task = current;							\
> > +} while (0)
> > +#else
> > +# define INIT_WQ_BARRIER_ONSTACK(barr, func, target)				\
> > +do {										\
> > +	INIT_WORK_ONSTACK(&(barr)->work, func);					\
> > +	__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&(barr)->work));	\
> > +	init_completion(&barr->done);						\
> > +	barr->task = current;							\
> > +} while (0)
> > +#endif
> 
> Is there any progress with this bug? This false positive warning regression is 
> blocking the locking tree.
> 

I have been trying to reproduce the false positive on my machine, but
haven't succeeded. ;-( Have you tried this?

But I have been using this patch for a day and haven't shoot my foot
yet.

> BTW., I don't think the #ifdef is necessary: lockdep_init_map_crosslock should map 
> to nothing when lockdep is disabled, right?

IIUC, lockdep_init_map_crosslock is only defined when
CONFIG_LOCKDEP_CROSSRELEASE=y, moreover, completion::map, which used as
the parameter of lockdep_init_map_crosslock(), is only defined when
CONFIG_LOCKDEP_COMPLETE=y. So the #ifdef is necessary, but maybe we can
clean this thing up in the future.

I will send a proper patch, so the thing could move forwards. Just a
minute ;-)

Regards,
Boqun

> 
> Thanks,
> 
> 	Ingo

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