linux-kernel - Re: [syzbot] [mm?] general protection fault in hpage_collapse_scan

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Date: Tue, 9 Apr 2024 16:46:27 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: syzbot <syzbot+57adb2a4b9d206521bc2@...kaller.appspotmail.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] general protection fault in
 hpage_collapse_scan_file

On Tue, 09 Apr 2024 03:16:20 -0700 syzbot <syzbot+57adb2a4b9d206521bc2@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    8568bb2ccc27 Add linux-next specific files for 20240405
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=152f4805180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=48ca5acf8d2eb3bc
> dashboard link: https://syzkaller.appspot.com/bug?extid=57adb2a4b9d206521bc2
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1268258d180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1256598d180000

Help.  From a quick look this seems to be claiming that collapse_file()
got to 

	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);

with folio==NULL, but the code look solid regarding this.

Given that we have a reproducer, can we expect the bot to perform a
bisection for us?