linux-kernel - Re: [syzbot] [mm?] WARNING: bad unlock balance in madvise_cold_or_pageout_pte

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Date: Thu,  4 Apr 2024 19:44:50 +0800
From: Hillf Danton <hdanton@...a.com>
To: syzbot <syzbot+c641706ad4e9688cccdf@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING: bad unlock balance in madvise_cold_or_pageout_pte_range

On Thu, 04 Apr 2024 03:56:24 -0700
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    727900b675b7 Add linux-next specific files for 20240403
> git tree:       linux-next
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13764a3d180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  727900b675b7

--- x/mm/madvise.c
+++ y/mm/madvise.c
@@ -482,10 +482,7 @@ restart:
 				err = split_folio(folio);
 				folio_unlock(folio);
 				folio_put(folio);
-				if (err)
-					continue;
-				start_pte = pte =
-					pte_offset_map_lock(mm, pmd, addr, &ptl);
+				start_pte = pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
 				if (!start_pte)
 					break;
 				arch_enter_lazy_mmu_mode();
--