Re: in_irq_or_nmi() and RFC patch

From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>,
	Pankaj Gupta <pagupta@redhat.com>,
	Tariq Toukan <ttoukan.linux@gmail.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Tariq Toukan <tariqt@mellanox.com>,
	netdev@vger.kernel.org, akpm@linux-foundation.org,
	linux-mm <linux-mm@kvack.org>,
	Saeed Mahameed <saeedm@mellanox.com>,
	linux-kernel@vger.kernel.org, brouer@redhat.com
Subject: Re: in_irq_or_nmi() and RFC patch
Date: Thu, 30 Mar 2017 09:12:23 +0200	[thread overview]
Message-ID: <20170330091223.05aa0efe@redhat.com> (raw)
In-Reply-To: <20170330064958.uxih6ik5fkwvjqf6@hirez.programming.kicks-ass.net>

On Thu, 30 Mar 2017 08:49:58 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Mar 29, 2017 at 09:44:41PM +0200, Jesper Dangaard Brouer wrote:
> > @@ -2481,7 +2481,11 @@ void free_hot_cold_page(struct page *page, bool cold)
> >  	unsigned long pfn = page_to_pfn(page);
> >  	int migratetype;
> >  
> > -	if (in_interrupt()) {
> > +	/*
> > +	 * Exclude (hard) IRQ and NMI context from using the pcplists.
> > +	 * But allow softirq context, via disabling BH.
> > +	 */
> > +	if (in_irq() || irqs_disabled()) {  
> 
> Why do you need irqs_disabled() ? 

Because further down I call local_bh_enable(), which calls
__local_bh_enable_ip() which triggers a warning during early boot on:

  WARN_ON_ONCE(in_irq() || irqs_disabled());

It looks like it is for supporting CONFIG_TRACE_IRQFLAGS.

> Also, your comment is stale, it still refers to NMI context.

True, as you told me NMI is implicit, as it cannot occur.

> >  		__free_pages_ok(page, 0);
> >  		return;
> >  	}  

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer