netdev - Re: in_irq_or_nmi() and RFC patch

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Date:   Thu, 30 Mar 2017 09:12:23 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Pankaj Gupta <pagupta@...hat.com>,
        Tariq Toukan <ttoukan.linux@...il.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tariq Toukan <tariqt@...lanox.com>, netdev@...r.kernel.org,
        akpm@...ux-foundation.org, linux-mm <linux-mm@...ck.org>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-kernel@...r.kernel.org, brouer@...hat.com
Subject: Re: in_irq_or_nmi() and RFC patch

On Thu, 30 Mar 2017 08:49:58 +0200
Peter Zijlstra <peterz@...radead.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