+ mm-compaction-fix-fast_isolate_around-to-stay-within-boundaries.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm, compaction: fix fast_isolate_around() to stay within boundaries
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-compaction-fix-fast_isolate_around-to-stay-within-boundaries.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-compaction-fix-fast_isolate_around-to-stay-within-boundaries.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: NARIBAYASHI Akira <a.naribayashi@fujitsu.com>
Subject: mm, compaction: fix fast_isolate_around() to stay within boundaries
Date: Wed, 26 Oct 2022 20:24:38 +0900

Depending on the memory configuration, isolate_freepages_block() may scan
pages out of the target range and causes panic.

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 6e2b7044c199 ("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: 6e2b7044c199 ("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>
---


--- a/mm/compaction.c~mm-compaction-fix-fast_isolate_around-to-stay-within-boundaries
+++ a/mm/compaction.c
@@ -1344,7 +1344,7 @@ move_freelist_tail(struct list_head *fre
 }
 
 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_contr
 	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_co
 		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;
 }
 
_

Patches currently in -mm which might be from a.naribayashi@fujitsu.com are

mm-compaction-fix-fast_isolate_around-to-stay-within-boundaries.patch