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Date:   Tue, 13 Mar 2018 11:55:49 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Pavel Tatashin <pasha.tatashin@oracle.com>
Cc:     steven.sistare@oracle.com, daniel.m.jordan@oracle.com,
        m.mizuma@jp.fujitsu.com, mhocko@suse.com, catalin.marinas@arm.com,
        takahiro.akashi@linaro.org, gi-oh.kim@profitbricks.com,
        heiko.carstens@de.ibm.com, baiyaowei@cmss.chinamobile.com,
        richard.weiyang@gmail.com, paul.burton@mips.com,
        miles.chen@mediatek.com, vbabka@suse.cz, mgorman@suse.de,
        hannes@cmpxchg.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org
Subject: Re: [v5 1/2] mm: disable interrupts while initializing deferred
 pages
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        <20180312130410.e2fce8e5e38bc2086c7fd924@linux-foundation.org>
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On Tue, 13 Mar 2018 12:04:30 -0400 Pavel Tatashin <pasha.tatashin@oracle.com> wrote:

> > 
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1506,7 +1506,6 @@ static void __init deferred_free_pages(int nid, int zid, unsigned long pfn,
> > >  		} else if (!(pfn & nr_pgmask)) {
> > >  			deferred_free_range(pfn - nr_free, nr_free);
> > >  			nr_free = 1;
> > > -			cond_resched();
> > >  		} else {
> > >  			nr_free++;
> > 
> > And how can we simply remove these cond_resched()s?  I assume this is
> > being done because interrupts are now disabled?  But those were there
> > for a reason, weren't they?
> 
> We must remove cond_resched() because we can't sleep anymore. They were
> added to fight NMI timeouts, so I will replace them with
> touch_nmi_watchdog() in a follow-up fix.

This makes no sense.  Any code section where we can add cond_resched()
was never subject to NMI timeouts because that code cannot be running with
disabled interrupts.