linux-kernel - Re: [PATCH stable] tick/nohz: Prevent bogus softirq pending warning

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Date:   Wed, 12 Sep 2018 15:56:04 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Crispin <john@...ozen.org>, frederic@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH stable] tick/nohz: Prevent bogus softirq pending warning

Hi Thomas,

On Thu, Aug 30, 2018 at 5:06 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> Commit 0a0e0829f990 ("nohz: Fix missing tick reprogram when interrupting an
> inline softirq") got backported to stable trees and now causes the NOHZ
> softirq pending warning to trigger. It's not an upstream issue as the NOHZ
> update logic has been changed there.
>
> The problem is when a softirq disabled section gets interrupted and on
> return from interrupt the tick/nohz state is evaluated, which then can
> observe pending soft interrupts. These soft interrupts are legitimately
> pending because they cannot be processed as long as soft interrupts are
> disabled and the interrupted code will correctly process them when soft
> interrupts are reenabled.
>
> Add a check for softirqs disabled to the pending check to prevent the
> warning.
>
> Reported-by: Grygorii Strashko <grygorii.strashko@...com>
> Reported-by: John Crispin <john@...ozen.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Tested-by: Grygorii Strashko <grygorii.strashko@...com>
> Tested-by: John Crispin <john@...ozen.org>
> Cc: Frederic Weisbecker <frederic@...nel.org>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Anna-Maria Gleixner <anna-maria@...utronix.de>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: stable@...r.kernel.org

Fixes: 2d898915ccf4838c ("nohz: Fix missing tick reprogram when
interrupting an inline softirq")

Issue in v4.14.x bisected to the above commit, and fixed by your patch.

Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds