mm, compaction: fix fast_isolate_around() to stay within boundaries

nariba-fj · akpm00 · commit be21b32afe47 · 2022-11-30T15:59:07.000-08:00
Depending on the memory configuration, isolate_freepages_block() may scan pages out of the target range and causes panic. Panic can occur on systems with multiple zones in a single pageblock. The reason it is rare is that it only happens in special configurations. Depending on how many similar systems there are, it may be a good idea to fix this problem for older kernels as well. The problem is that pfn as argument of fast_isolate_around() could be out of the target range. Therefore we should consider the case where pfn < start_pfn, and also the case where end_pfn < pfn. This problem should have been addressd by the commit 6e2b704 ("mm, compaction: make fast_isolate_freepages() stay within zone") but there was an oversight. Case1: pfn < start_pfn <at memory compaction for node Y> | node X's zone | node Y's zone +-----------------+------------------------------... pageblock ^ ^ ^ +-----------+-----------+-----------+-----------+... ^ ^ ^ ^ ^ end_pfn ^ start_pfn = cc->zone->zone_start_pfn pfn <---------> scanned range by "Scan After" Case2: end_pfn < pfn <at memory compaction for node X> | node X's zone | node Y's zone +-----------------+------------------------------... pageblock ^ ^ ^ +-----------+-----------+-----------+-----------+... ^ ^ ^ ^ ^ pfn ^ end_pfn start_pfn <---------> scanned range by "Scan Before" It seems that there is no good reason to skip nr_isolated pages just after given pfn. So let perform simple scan from start to end instead of dividing the scan into "Before" and "After". Link: https://lkml.kernel.org/r/20221026112438.236336-1-a.naribayashi@fujitsu.com Fixes: 6e2b704 ("mm, compaction: make fast_isolate_freepages() stay within zone"). Signed-off-by: NARIBAYASHI Akira <a.naribayashi@fujitsu.com> Cc: David Rientjes <rientjes@google.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
diff --git a/mm/compaction.c b/mm/compaction.c
@@ -1344,7 +1344,7 @@ move_freelist_tail(struct list_head *freelist, struct page *freepage)
 }
 
 static void
-fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
+fast_isolate_around(struct compact_control *cc, unsigned long pfn)
 {
 	unsigned long start_pfn, end_pfn;
 	struct page *page;
@@ -1365,21 +1365,13 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long
 	if (!page)
 		return;
 
-	/* Scan before */
-	if (start_pfn != pfn) {
-		isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
-		if (cc->nr_freepages >= cc->nr_migratepages)
-			return;
-	}
-
-	/* Scan after */
-	start_pfn = pfn + nr_isolated;
-	if (start_pfn < end_pfn)
-		isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
+	isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
 
 	/* Skip this pageblock in the future as it's full or nearly full */
 	if (cc->nr_freepages < cc->nr_migratepages)
 		set_pageblock_skip(page);
+
+	return;
 }
 
 /* Search orders in round-robin fashion */
@@ -1556,7 +1548,7 @@ fast_isolate_freepages(struct compact_control *cc)
 		return cc->free_pfn;
 
 	low_pfn = page_to_pfn(page);
-	fast_isolate_around(cc, low_pfn, nr_isolated);
+	fast_isolate_around(cc, low_pfn);
 	return low_pfn;
 }
 
