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

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Date:   Thu, 30 Aug 2018 17:12:54 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     John Crispin <john@...ozen.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH stable] tick/nohz: Prevent bogus softirq pending warning

On Thu, Aug 30, 2018 at 05:05:19PM +0200, Thomas Gleixner 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>

Acked-by: Frederic Weisbecker <frederic@...nel.org>

Thanks for cooking the patch!