linux-kernel - Re: [PATCH 09/32] locking/lockdep: Save stack trace for each softirq vector involved

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Message-ID: <20190213151854.GE8524@lenoir>
Date:   Wed, 13 Feb 2019 16:18:55 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 09/32] locking/lockdep: Save stack trace for each softirq
 vector involved

On Tue, Feb 12, 2019 at 09:47:39AM -0800, Linus Torvalds wrote:
> On Tue, Feb 12, 2019 at 9:15 AM Frederic Weisbecker <frederic@...nel.org> wrote:
> >
> >
> > +static int save_trace_mask(struct lock_class *class, u64 mask)
> > +{
> > +       int bit = 0;
> > +
> > +       while (mask) {
> > +               long fs = __ffs64(mask) + 1;
> > +
> > +               mask >>= fs;
> > +               bit += fs;
> 
> Same buggy pattern of "ffs+1" and overflow of shift count.

You're right and there are more. I'll unify all that around
a safe iterator.

Thanks.