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Date: Wed, 26 Aug 2015 14:51:26 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: David Rientjes <rientjes@google.com>
Cc: Yinghai Lu <yinghai@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Tony Luck <tony.luck@intel.com>, linux-kernel@vger.kernel.org,
	stable@vger.kernel.org
Subject: Re: [PATCH v3] mm: Check if section present during memory block
 registering
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On Wed, 26 Aug 2015 14:38:35 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:

> > --- linux-2.6.orig/drivers/base/node.c
> > +++ linux-2.6/drivers/base/node.c
> > @@ -390,7 +390,18 @@ int register_mem_sect_under_node(struct
> >  	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
> >  	sect_end_pfn += PAGES_PER_SECTION - 1;
> >  	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
> > -		int page_nid;
> > +		int page_nid, scn_nr;
> > +
> > +		/*
> > +		 * memory block could have several absent sections from start.
> > +		 * skip pfn range from absent section
> > +		 */
> > +		scn_nr = pfn_to_section_nr(pfn);
> > +		if (!present_section_nr(scn_nr)) {
> > +			pfn = round_down(pfn + PAGES_PER_SECTION,
> > +					 PAGES_PER_SECTION) - 1;
> > +			continue;
> > +		}
> >  
> >  		page_nid = get_nid_for_pfn(pfn);
> >  		if (page_nid < 0)
> 
> scn_nr should really be unsigned long, but it would probably be better to 
> simply use if (!pfn_present(pfn)) rather than store the section number.

Yup.  I was feeling lazy but you motivated me.

<grunt, wheeze>

--- a/drivers/base/node.c~mm-check-if-section-present-during-memory-block-registering-fix
+++ a/drivers/base/node.c
@@ -390,14 +390,13 @@ int register_mem_sect_under_node(struct
 	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
 	sect_end_pfn += PAGES_PER_SECTION - 1;
 	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
-		int page_nid, scn_nr;
+		int page_nid;
 
 		/*
 		 * memory block could have several absent sections from start.
 		 * skip pfn range from absent section
 		 */
-		scn_nr = pfn_to_section_nr(pfn);
-		if (!present_section_nr(scn_nr)) {
+		if (!present_section_nr(pfn_to_section_nr(pfn))) {
 			pfn = round_down(pfn + PAGES_PER_SECTION,
 					 PAGES_PER_SECTION) - 1;
 			continue;
_