linux-kernel - Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature

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Message-ID: <20170424051102.GJ21430@X58A-UD3R>
Date:   Mon, 24 Apr 2017 14:11:02 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
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,
        willy@...radead.org, npiggin@...il.com, kernel-team@....com
Subject: Re: [PATCH v6 05/15] lockdep: Implement crossrelease feature

On Wed, Apr 19, 2017 at 04:25:03PM +0200, Peter Zijlstra wrote:
> On Tue, Mar 14, 2017 at 05:18:52PM +0900, Byungchul Park wrote:
> > +struct hist_lock {
> > +	/*
> > +	 * Each work of workqueue might run in a different context,
> > +	 * thanks to concurrency support of workqueue. So we have to
> > +	 * distinguish each work to avoid false positive.
> > +	 */
> > +	unsigned int		work_id;
> >  };
> 
> > @@ -1749,6 +1749,14 @@ struct task_struct {
> >  	struct held_lock held_locks[MAX_LOCK_DEPTH];
> >  	gfp_t lockdep_reclaim_gfp;
> >  #endif
> > +#ifdef CONFIG_LOCKDEP_CROSSRELEASE
> > +#define MAX_XHLOCKS_NR 64UL
> > +	struct hist_lock *xhlocks; /* Crossrelease history locks */
> > +	unsigned int xhlock_idx;
> > +	unsigned int xhlock_idx_soft; /* For backing up at softirq entry */
> > +	unsigned int xhlock_idx_hard; /* For backing up at hardirq entry */
> > +	unsigned int work_id;
> > +#endif
> >  #ifdef CONFIG_UBSAN
> >  	unsigned int in_ubsan;
> >  #endif
> 
> > +/*
> > + * Crossrelease needs to distinguish each work of workqueues.
> > + * Caller is supposed to be a worker.
> > + */
> > +void crossrelease_work_start(void)
> > +{
> > +	if (current->xhlocks)
> > +		current->work_id++;
> > +}
> 
> > +/*
> > + * Only access local task's data, so irq disable is only required.
> > + */
> > +static int same_context_xhlock(struct hist_lock *xhlock)
> > +{
> > +	struct task_struct *curr = current;
> > +
> > +	/* In the case of hardirq context */
> > +	if (curr->hardirq_context) {
> > +		if (xhlock->hlock.irq_context & 2) /* 2: bitmask for hardirq */
> > +			return 1;
> > +	/* In the case of softriq context */
> > +	} else if (curr->softirq_context) {
> > +		if (xhlock->hlock.irq_context & 1) /* 1: bitmask for softirq */
> > +			return 1;
> > +	/* In the case of process context */
> > +	} else {
> > +		if (xhlock->work_id == curr->work_id)
> > +			return 1;
> > +	}
> > +	return 0;
> > +}
> 
> I still don't like work_id; it doesn't have anything to do with
> workqueues per se, other than the fact that they end up using it.
> 
> It's a history generation id; touching it completely invalidates our
> history. Workqueues need this because they run independent work from the
> same context.
> 
> But the same is true for other sites. Last time I suggested
> lockdep_assert_empty() to denote all suck places (and note we already
> have lockdep_sys_exit() that hooks into the return to user path).

I'm sorry but I don't understand what you intend. It would be appriciated
if you explain more.

You might know why I introduced the 'work_id'.. Is there any alternative?

Thank you.