linux-kernel - RE: [EXT] Re: [PATCH] softirq: add irq off checking for __raise_softirq

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Date:   Fri, 14 Aug 2020 03:28:58 +0000
From:   Jiafei Pan <jiafei.pan@....com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     "mingo@...nel.org" <mingo@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "romain.perier@...il.com" <romain.perier@...il.com>,
        "will@...nel.org" <will@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        Leo Li <leoyang.li@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Jiafei Pan <jiafei.pan@....com>
Subject: RE: [EXT] Re: [PATCH] softirq: add irq off checking for
 __raise_softirq_irqoff

> From: Peter Zijlstra <peterz@...radead.org>
> Sent: Thursday, August 13, 2020 1:58 PM
> 
> On Thu, Aug 06, 2020 at 12:07:29PM +0800, Jiafei Pan wrote:
> > __raise_softirq_irqoff will update per-CPU mask of pending softirqs,
> > it need to be called in irq disabled context in order to keep it
> > atomic operation, otherwise it will be interrupted by hardware
> > interrupt, and per-CPU softirqs pending mask will be corrupted, the
> > result is there will be unexpected issue, for example hrtimer soft irq
> > will be losed and soft hrtimer will never be expire and handled.
> >
> > Adding irqs disabled checking here to provide warning in irqs enabled
> > context.
> >
> > Signed-off-by: Jiafei Pan <Jiafei.Pan@....com>
> > ---
> >  kernel/softirq.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/kernel/softirq.c b/kernel/softirq.c index
> > bf88d7f62433..11f61e54a3ae 100644
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -481,6 +481,11 @@ void raise_softirq(unsigned int nr)
> >
> >  void __raise_softirq_irqoff(unsigned int nr)  {
> > +     /* This function can only be called in irq disabled context,
> > +      * otherwise or_softirq_pending will be interrupted by hardware
> > +      * interrupt, so that there will be unexpected issue.
> > +      */
> 
> Comment style is wrong, also I'm not sure the comment is really helpfull.
[Jiafei Pan] Thanks for your comments, yes, function name already indicate the function
Should be called in irq off context, will remove the comment in next version.
> 
> > +     WARN_ON_ONCE(!irqs_disabled());
> 
>         lockdep_assert_irqs_disabled();
> 
> >       trace_softirq_raise(nr);
> >       or_softirq_pending(1UL << nr);
> >  }