Re: [BISECTED] first bad commit is c203c6d5b3f0597 ("migrate_pages: batch _unmap and _move")

["Huang, Ying" <ying.huang@intel.com>]

"Huang, Ying" <ying.huang@intel.com> writes:

> Hi, Hyeonggon,
>
> Hyeonggon Yoo <42.hyeyoo@gmail.com> writes:
>
>> On Wed, Feb 01, 2023 at 01:09:10AM +0900, Hyeonggon Yoo wrote:
>>> I've observed random list_del corruption on mm-unstable,
>>> where HEAD is commit d69862e693c069f4
>>> ("mm/migrate: convert putback_movable_pages() to use folios").
>>> 
>>> The issue can be easily reproduced by stressing MM multiple times:
>>> 	stress-ng --bigheap 0 --timeout 300
>>> 
>>> The compiler is gcc 12.2.1 and config, dmesg are included as attachment.
>>> I will try to bisect but can't promise quick resolution :)
>>
>>
>> The first bad commits appears to be:
>> c203c6d5b3f0597 ("migrate_pages: batch _unmap and _move")
>>
>> the first bad commit _probably_ be earlier, but this is quite
>> easy to reproduce so at this point I think above is the real bad commit.
>
> Thank you very much for reporting the bug.  I'm in travel now but I will
> try to find some time to reproduce and debug it.

Still haven't reproduced the issue.  But after reviewing the code, I
found a bug in the code, which may cause list corruption.  Can you try
the debug patch below?

Best Regards,
Huang, Ying

-------------------------------8<-------------------------------------
From a4eef847fe4f6e50b6c3f69651c1dfdeb4b23bc4 Mon Sep 17 00:00:00 2001
From: Huang Ying <ying.huang@intel.com>
Date: Fri, 3 Feb 2023 07:12:24 +0800
Subject: [PATCH] dbg: fix list corruption for -EAGAIN

---
 mm/migrate.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 143d96775b4d..4205a0297ef8 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1230,11 +1230,11 @@ static int __migrate_folio_move(struct folio *src, struct folio *dst,
 
 	rc = move_to_new_folio(dst, src, mode);
 
-	if (rc != -EAGAIN)
+	if (rc != -EAGAIN) {
 		list_del(&dst->lru);
-
-	if (unlikely(!is_lru))
-		goto out_unlock_both;
+		if (unlikely(!is_lru))
+			goto out_unlock_both;
+	}
 
 	/*
 	 * When successful, push dst to LRU immediately: so that if it
-- 
2.35.1