linux-kernel - Re: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks)

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Date:	Mon, 13 Jan 2014 17:07:05 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: check && lockdep_no_validate (Was: lockdep: Introduce
	wait-type checks)

On 01/12, Peter Zijlstra wrote:
>
> On Thu, Jan 09, 2014 at 06:54:48PM +0100, Oleg Nesterov wrote:
> >
> > --- a/kernel/locking/lockdep.c
> > +++ b/kernel/locking/lockdep.c
> > @@ -1939,7 +1939,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
> >  		 * Only non-recursive-read entries get new dependencies
> >  		 * added:
> >  		 */
> > -		if (hlock->read != 2) {
> > +		if (hlock->read != 2 &&
> > +		    hlock->instance->key != &__lockdep_no_validate__) {
> >  			if (!check_prev_add(curr, hlock, next,
> >  						distance, trylock_loop))
> >  				return 0;
> >
>
> Hmm, you are quite right indeed;

Thanks!

> although I would write it like:
>
>   if (hlock->read != 2 && hlock->check == 2)
>
> because the __lockdep_no_validate__ thing forces the ->check value to 1.

Agreed, hlock->check == 2 looks better. But this connects to another
patch I sent which removes hlock->check...

OK, I'll wait for review on that patch, then resend this one with
->check or __lockdep_no_validate__ depending on the result.

Oleg.

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