From 60177d31d215bc2b4c5a7aa6f742800e04fa0a92 Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Thu, 6 Dec 2012 19:01:14 +0000 Subject: [PATCH] mm: compaction: validate pfn range passed to isolate_freepages_block Commit 0bf380bc70ec ("mm: compaction: check pfn_valid when entering a new MAX_ORDER_NR_PAGES block during isolation for migration") added a check for pfn_valid() when isolating pages for migration as the scanner does not necessarily start pageblock-aligned. Since commit c89511ab2f8f ("mm: compaction: Restart compaction from near where it left off"), the free scanner has the same problem. This patch makes sure that the pfn range passed to isolate_freepages_block() is within the same block so that pfn_valid() checks are unnecessary. In answer to Henrik's wondering why others have not reported this: reproducing this requires a large enough hole with the right aligment to have compaction walk into a PFN range with no memmap. Size and alignment depends in the memory model - 4M for FLATMEM and 128M for SPARSEMEM on x86. It needs a "lucky" machine. Reported-by: Henrik Rydberg Signed-off-by: Mel Gorman Signed-off-by: Linus Torvalds --- mm/compaction.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/mm/compaction.c b/mm/compaction.c index 9eef55838fca..694eaabaaebd 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -713,7 +713,15 @@ static void isolate_freepages(struct zone *zone, /* Found a block suitable for isolating free pages from */ isolated = 0; - end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn); + + /* + * As pfn may not start aligned, pfn+pageblock_nr_page + * may cross a MAX_ORDER_NR_PAGES boundary and miss + * a pfn_valid check. Ensure isolate_freepages_block() + * only scans within a pageblock + */ + end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); + end_pfn = min(end_pfn, zone_end_pfn); isolated = isolate_freepages_block(cc, pfn, end_pfn, freelist, false); nr_freepages += isolated; -- 2.30.2