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

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Date:   Thu, 27 Sep 2018 10:48:17 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
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>,
        Thomas Gleixner <tglx@...utronix.de>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH stable] tick/nohz: Prevent bogus softirq pending warning

On Thu, Sep 27, 2018 at 10:07:39AM +0200, Geert Uytterhoeven wrote:
> Hi Greg,
> 
> On Wed, Sep 12, 2018 at 3:56 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> > 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>
> 
> This issue is still present in v4.14.72. Can you please apply Thomas' fix?

Oops, sorry for the delay, now queued up.

greg k-h