[PATCH v3 3/6] mm/compaction: correctly return failure with bogus compound_order in strict mode

[Kemeng Shi]

In strict mode, we should return 0 if there is any hole in pageblock. If
we successfully isolated pages at beginning at pageblock and then have a
bogus compound_order outside pageblock in next page. We will abort search
loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
we will treat it as a successful isolation in strict mode as blockpfn is
not < end_pfn and return partial isolated pages. Then
isolate_freepages_range may success unexpectly with hole in isolated
range.

Fixes: 9fcd6d2e052e ("mm, compaction: skip compound pages by order in free scanner")
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/compaction.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index a40550a33aee..9ecbfbc695e5 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -626,11 +626,12 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 		if (PageCompound(page)) {
 			const unsigned int order = compound_order(page);
 
-			if (likely(order <= MAX_ORDER)) {
+			if (blockpfn + (1UL << order) <= end_pfn) {
 				blockpfn += (1UL << order) - 1;
 				page += (1UL << order) - 1;
 				nr_scanned += (1UL << order) - 1;
 			}
+
 			goto isolate_fail;
 		}
 
@@ -678,8 +679,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 		spin_unlock_irqrestore(&cc->zone->lock, flags);
 
 	/*
-	 * There is a tiny chance that we have read bogus compound_order(),
-	 * so be careful to not go outside of the pageblock.
+	 * Be careful to not go outside of the pageblock.
 	 */
 	if (unlikely(blockpfn > end_pfn))
 		blockpfn = end_pfn;
-- 
2.30.0