linux-kernel - [PATCH] mm/memory_hotplug: fix dead loop in offline

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Date:   Fri, 28 Apr 2023 18:08:46 +0800
From:   Yajun Deng <yajun.deng@...ux.dev>
To:     david@...hat.com, osalvador@...e.de, akpm@...ux-foundation.org,
        mhocko@...e.com
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Yajun Deng <yajun.deng@...ux.dev>
Subject: [PATCH] mm/memory_hotplug: fix dead loop in offline_pages()

When migration failure in do_migrate_range() and then the
scan_movable_pages() will most likely return the same movable pfn.
In this case, there is no condition to bail out, they will
always run like this:

...
[878020.623959] migrating pfn 1727813 failed ret:1
[878020.623960] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
[878020.623962] memcg:ffffa0ff82d5a000
[878020.623962] aops:def_blk_aops ino:fd00001
[878020.623964] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
[878020.623966] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
[878020.623967] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
[878020.623968] page dumped because: migration failure
[878020.626196] migrating pfn 1727813 failed ret:1
[878020.626198] page:00000000faa9673c refcount:3 mapcount:0 mapping:00000000144ccd79 index:0x14280025 pfn:0x1727813
[878020.626200] memcg:ffffa0ff82d5a000
[878020.626200] aops:def_blk_aops ino:fd00001
[878020.626202] flags: 0x17ffffc000206a(referenced|dirty|active|workingset|private|node=0|zone=2|lastcpupid=0x1fffff)
[878020.626204] raw: 0017ffffc000206a ffffb0d14f50fbd8 ffffb0d14f50fbd8 ffffa0ff9c155018
[878020.626205] raw: 0000000014280025 ffffa10327d702d8 00000003ffffffff ffffa0ff82d5a000
[878020.626206] page dumped because: migration failure
...

Bail out when migration failures reach 3 times.

Fixes: bb8965bd82fd ("mm, memory_hotplug: deobfuscate migration part of offlining")
Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
---
 mm/memory_hotplug.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8e0fa209d533..72dd385b8892 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1800,11 +1800,12 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 			struct zone *zone, struct memory_group *group)
 {
 	const unsigned long end_pfn = start_pfn + nr_pages;
-	unsigned long pfn, system_ram_pages = 0;
+	unsigned long pfn, tmp_pfn, system_ram_pages = 0;
 	const int node = zone_to_nid(zone);
 	unsigned long flags;
 	struct memory_notify arg;
 	char *reason;
+	int count = 0;
 	int ret;
 
 	/*
@@ -1887,12 +1888,20 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
 
 			cond_resched();
 
+			tmp_pfn = pfn;
 			ret = scan_movable_pages(pfn, end_pfn, &pfn);
 			if (!ret) {
-				/*
-				 * TODO: fatal migration failures should bail
-				 * out
-				 */
+				if (pfn == tmp_pfn)
+					count++;
+				else
+					count = 0;
+
+				if (unlikely(count == 3)) {
+					ret = -EBUSY;
+					reason = "migration failure";
+					goto failed_removal_isolated;
+				}
+
 				do_migrate_range(pfn, end_pfn);
 			}
 		} while (!ret);
-- 
2.25.1