linux-kernel - Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all part of PROVE

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Date:   Wed, 23 Aug 2017 11:12:17 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Chinner <david@...morbit.com>, mingo@...nel.org,
        linux-kernel@...r.kernel.org, kernel-team@....com,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Tejun Heo <tj@...nel.org>, Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v3 1/3] lockdep: Make LOCKDEP_CROSSRELEASE configs all
 part of PROVE_LOCKING

On Tue, Aug 22, 2017 at 11:37:03AM +0200, Peter Zijlstra wrote:
> On Tue, Aug 22, 2017 at 06:22:36PM +0900, Byungchul Park wrote:
> > On Tue, Aug 22, 2017 at 11:06:03AM +0200, Peter Zijlstra wrote:
> > > So I did the below little hack, which basically wipes the entire lock
> > > history when we start a work and thereby disregards/looses the
> > > dependency on the work 'lock'.
> > > 
> > > It makes my test box able to boot and build a kernel on XFS, so while I
> > > see what you're saying (I think), it doesn't appear to instantly show.
> > > 
> > > Should I run xfstests or something to further verify things are OK? Does
> > > that need a scratch partition (I keep forgetting how to run that stuff
> > > :/).
> > > 
> > > ---
> > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> > > index 66011c9f5df3..de91cdce9460 100644
> > > --- a/kernel/locking/lockdep.c
> > > +++ b/kernel/locking/lockdep.c
> > > @@ -4756,10 +4756,14 @@ void crossrelease_hist_start(enum xhlock_context_t c)
> > >  {
> > >  	struct task_struct *cur = current;
> > >  
> > > -	if (cur->xhlocks) {
> > > -		cur->xhlock_idx_hist[c] = cur->xhlock_idx;
> > > -		cur->hist_id_save[c] = cur->hist_id;
> > > -	}
> > > +	if (!cur->xhlocks)
> > > +		return;
> > > +
> > > +	if (c == XHLOCK_PROC)
> > > +		invalidate_xhlock(&xhlock(cur->xhlock_idx));
> > 
> > We have to detect dependecies if it exists, even in the following case:
> > 
> > oooooooiiiiiiiiiiiiiiiiiii.........
> >   |<- range for commit ->|
> > 
> >   where
> >   o: acquisition outside of each work,
> >   i: acquisition inside of each work,
> > 
> > With yours, we can never detect dependecies wrt 'o'.
> 
> There really shouldn't be any o's when you call

There can be any o's.

> crossrelease_hist_start(XHLOCK_PROC), it should denote the bottom of a

No, I don't think so. It can be either the bottom or not.

hist_start() and hist_end() is only for special contexts which need roll
back on exit e.g. irq, work and so on. Normal kernel context should work
well w/o hist_start() or hist_end().

> context, see:
> 
>   https://lkml.kernel.org/r/20170301104328.GD6515@twins.programming.kicks-ass.net

Actually, I don't agree with that.

> And in that respect you placed the calls wrongly in process_one_work(),

Why is it wrong? It's intended. Could you tell me why?