linux-kernel - Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature

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Date:   Tue, 28 Feb 2017 14:35:21 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Byungchul Park <byungchul.park@....com>
Cc:     mingo@...nel.org, tglx@...utronix.de, walken@...gle.com,
        boqun.feng@...il.com, kirill@...temov.name,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        npiggin@...il.com, kernel-team@....com
Subject: Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature

On Tue, Feb 28, 2017 at 10:28:20PM +0900, Byungchul Park wrote:
> On Tue, Feb 28, 2017 at 02:05:13PM +0100, Peter Zijlstra wrote:
> > On Wed, Jan 18, 2017 at 10:17:32PM +0900, Byungchul Park wrote:
> > > +#define MAX_XHLOCKS_NR 64UL
> > 
> > > +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> > > +	if (tsk->xhlocks) {
> > > +		void *tmp = tsk->xhlocks;
> > > +		/* Disable crossrelease for current */
> > > +		tsk->xhlocks = NULL;
> > > +		vfree(tmp);
> > > +	}
> > > +#endif
> > 
> > > +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> > > +	p->xhlock_idx = 0;
> > > +	p->xhlock_idx_soft = 0;
> > > +	p->xhlock_idx_hard = 0;
> > > +	p->xhlock_idx_nmi = 0;
> > > +	p->xhlocks = vzalloc(sizeof(struct hist_lock) * MAX_XHLOCKS_NR);
> > 
> > I don't think we need vmalloc for this now.
> 
> Really? When is a better time to do it?
> 
> I think the time creating a task is the best time to initialize it. No?

The place is fine, but I would use kmalloc() now (and subsequently kfree
on the other end) for the allocation. Its not _that_ large anymore,
right?