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Message-ID: <20130110234258.GA15458@atomide.com>
Date: Thu, 10 Jan 2013 15:42:58 -0800
From: Tony Lindgren <tony@...mide.com>
To: Colin Cross <ccross@...roid.com>
Cc: lkml <linux-kernel@...r.kernel.org>,
Don Zickus <dzickus@...hat.com>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
liu chuansheng <chuansheng.liu@...el.com>,
Thomas Gleixner <tglx@...utronix.de>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] hardlockup: detect hard lockups without NMIs using
secondary cpus
* Colin Cross <ccross@...roid.com> [130110 14:37]:
> On Thu, Jan 10, 2013 at 12:38 PM, Tony Lindgren <tony@...mide.com> wrote:
> >
> > * Colin Cross <ccross@...roid.com> [130109 18:05]:
> > > +static void watchdog_check_hardlockup_other_cpu(void)
> > > +{
> > > + int cpu;
> > > + cpumask_t cpus = watchdog_cpus;
> > > +
> > > + /*
> > > + * Test for hardlockups every 3 samples. The sample period is
> > > + * watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
> > > + * watchdog_thresh (over by 20%).
> > > + */
> > > + if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
> > > + return;
> > > +
> > > + /* check for a hardlockup on the next cpu */
> > > + cpu = cpumask_next(smp_processor_id(), &cpus);
> >
> > Hmm don't you want to check cpu_oneline_mask here and
> > return if the other CPU is offline?
>
> watchdog_cpus is effectively a local copy of cpu_online_mask, but
> updated after the watchdog_nmi_touch in watchdog_nmi_enable. This
> avoids a false positive after hotplugging in a cpu when
> cpu_online_mask is true but that cpu hasn't yet run it's first
> hrtimer.
OK thanks for clarifying that.
Tony
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