linux-kernel - Re: [PATCH 2/5] kernel/watchdog_hld: clarify the condition in hardlockup_detector_event

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Message-ID: <YUK+O0QI4o0CoVeT@piliu.users.ipa.redhat.com>
Date:   Thu, 16 Sep 2021 11:47:07 +0800
From:   Pingfan Liu <piliu@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Pingfan Liu <kernelfans@...il.com>, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>, Wang Qing <wangqing@...o.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Santosh Sivaraj <santosh@...six.org>,
        Sumit Garg <sumit.garg@...aro.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 2/5] kernel/watchdog_hld: clarify the condition in
 hardlockup_detector_event_create()

On Tue, Sep 14, 2021 at 09:06:27PM -0700, Andrew Morton wrote:
> On Wed, 15 Sep 2021 11:51:00 +0800 Pingfan Liu <kernelfans@...il.com> wrote:
> 
> > hardlockup_detector_event_create() indirectly calls
> > kmem_cache_alloc_node(), which is blockable.
> > 
> > So here, the really planned context is is_percpu_thread().
> > 
> > ...
> >
> > --- a/kernel/watchdog_hld.c
> > +++ b/kernel/watchdog_hld.c
> > @@ -165,10 +165,13 @@ static void watchdog_overflow_callback(struct perf_event *event,
> >  
> >  static int hardlockup_detector_event_create(void)
> >  {
> > -	unsigned int cpu = smp_processor_id();
> > +	unsigned int cpu;
> >  	struct perf_event_attr *wd_attr;
> >  	struct perf_event *evt;
> >  
> > +	/* This function plans to execute in cpu bound kthread */
> > +	BUG_ON(!is_percpu_thread());
> 
> Can we avoid adding the BUG()?  Find a way to emit a WARNing and then
> permit the kernel to continue?
> 
Yes, WARN_ON() can work in this case.

Thanks,

	Pingfan