linux-kernel - [PATCH v2 3/7] mm/compaction: correctly return failure with bogus compound

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Message-Id: <20230826153617.4019189-4-shikemeng@huaweicloud.com>
Date:   Sat, 26 Aug 2023 23:36:13 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, baolin.wang@...ux.alibaba.com,
        mgorman@...hsingularity.net, david@...hat.com, willy@...radead.org
Cc:     shikemeng@...weicloud.com
Subject: [PATCH v2 3/7] mm/compaction: correctly return failure with bogus compound_order in strict mode

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: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 mm/compaction.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index a40550a33aee..b4d03c9ffe7c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -631,6 +631,14 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
 				page += (1UL << order) - 1;
 				nr_scanned += (1UL << order) - 1;
 			}
+			/*
+			 * There is a tiny chance that we have read bogus
+			 * compound_order(), so be careful to not go outside
+			 * of the pageblock.
+			 */
+			if (unlikely(blockpfn >= end_pfn))
+				blockpfn = end_pfn - 1;
+
 			goto isolate_fail;
 		}
 
@@ -678,8 +686,7 @@ 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