[patch 1/6] mm: page_isolation: check pfn validity before access

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From: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Subject: mm: page_isolation: check pfn validity before access

In the undo path of start_isolate_page_range(), we need to check the pfn
validity before accessing its page, or it will trigger an addressing
exception if there is hole in the zone.

This issue is found by code-review not a test-trigger.  In
"CONFIG_HOLES_IN_ZONE" environment, there is a certain chance that it
would casue an addressing exception when start_isolate_page_range()
fails, this could affect CMA, hugepage and memory-hotplug function.

Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Mel Gorman <mel@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_isolation.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff -puN mm/page_isolation.c~mm-page_isolation-check-pfn-validity-before-access mm/page_isolation.c
--- a/mm/page_isolation.c~mm-page_isolation-check-pfn-validity-before-access
+++ a/mm/page_isolation.c
@@ -176,8 +176,11 @@ int start_isolate_page_range(unsigned lo
 undo:
 	for (pfn = start_pfn;
 	     pfn < undo_pfn;
-	     pfn += pageblock_nr_pages)
-		unset_migratetype_isolate(pfn_to_page(pfn), migratetype);
+	     pfn += pageblock_nr_pages) {
+		page = __first_valid_page(pfn, pageblock_nr_pages);
+		if (page)
+			unset_migratetype_isolate(page, migratetype);
+	}
 
 	return -EBUSY;
 }
_
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