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

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Date:   Tue, 12 Feb 2019 09:47:39 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Frederic Weisbecker <frederic@...nel.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 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.

                 Linus