In isolate_freepages(), low_pfn was mistakenly initialized to
pageblock_start_pfn() instead of pageblock_end_pfn(), creating a possible
underflow, as described by Hugh:
There's a case when that "block_start_pfn -= pageblock_nr_pages" loop can
pass through 0 and end up trying to access a pageblock before the start of
the mem_map[].
Fixes: mmotm
mm-compaction-wrap-calculating-first-and-last-pfn-of-pageblock.patch
Reported-by: Hugh Dickins <hu...@google.com>
Signed-off-by: Vlastimil Babka <vba...@suse.cz>
---
mm/compaction.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 759c3ac73ced..6a49d1b35515 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -999,7 +999,7 @@ static void isolate_freepages(struct compact_control *cc)
block_start_pfn = pageblock_start_pfn(cc->free_pfn);
block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
zone_end_pfn(zone));
- low_pfn = pageblock_start_pfn(cc->migrate_pfn);
+ low_pfn = pageblock_end_pfn(cc->migrate_pfn);
/*
* Isolate free pages until enough are available to migrate the
--
2.8.1
