linux-kernel - Re: [PATCH v8 06/14] lockdep: Detect and handle hist

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Message-ID: <20170814072211.GK20323@X58A-UD3R>
Date:   Mon, 14 Aug 2017 16:22:11 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Byungchul Park <max.byungchul.park@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, tglx@...utronix.de,
        Michel Lespinasse <walken@...gle.com>, kirill@...temov.name,
        "linux-kernel@...r.kernel.org" <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 06/14] lockdep: Detect and handle hist_lock ring
 buffer overwrite

On Mon, Aug 14, 2017 at 03:05:22PM +0800, Boqun Feng wrote:
> > I like Boqun's approach most but, _whatever_. It's ok if it solves the problem.
> > The last one is not bad when it is used for syscall exit, but we have to give
> > up valid dependencies unnecessarily in other cases. And I think Peterz's
> > approach should be modified a bit to make it work neatly, like:
> > 
> > crossrelease_hist_end(...)
> > {
> > ...
> >        invalidate_xhlock(&xhlock(cur->xhlock_idx_max));
> > 
> >        for (c = 0; c < XHLOCK_CXT_NR; c++)
> >               if ((cur->xhlock_idx_max - cur->xhlock_idx_hist[c]) >=
> > MAX_XHLOCKS_NR)
> >                      invalidate_xhlock(&xhlock(cur->xhlock_idx_hist[c]));
> > ...
> > }
> > 
> 
> Haven't looked into this deeply, but my gut feeling is this is
> unnecessary, will have a deep look.

Of course, for now, it looks like we can rely on the check_same_context()
on the commit, without invalidating it. But I think the approach might be
dangerous in future. I think it would be better to do it explicitlly.

> 
> Regards,
> Boqun
> 
> > And then Peterz's approach can also work, I think.
> > 
> > ---
> > Thanks,
> > Byungchul