Re: [syzbot] [net?] kernel BUG in filemap_fault (2)

[Hillf Danton <hdanton@sina.com>]

> Date: Thu, 03 Jul 2025 09:43:30 -0700
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    b4911fb0b060 Merge tag 'mmc-v6.16-rc1' of git://git.kernel..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=16568c8c580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3f6ddf055b5c86f8
> dashboard link: https://syzkaller.appspot.com/bug?extid=263f159eb37a1c4c67a4
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=157cf48c580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=146a948c580000

#syz test

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -3439,7 +3439,6 @@ retry_find:
 		folio_put(folio);
 		goto retry_find;
 	}
-	VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
 
 	/*
 	 * We have a locked folio in the page cache, now we need to check
@@ -3490,6 +3489,7 @@ retry_find:
 		return VM_FAULT_SIGBUS;
 	}
 
+	VM_BUG_ON_FOLIO(!folio_contains(folio, index), folio);
 	vmf->page = folio_file_page(folio, index);
 	return ret | VM_FAULT_LOCKED;
 
--