linux-kernel - Re: [syzbot] [mm?] WARNING in try_to_migrate

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Date: Mon, 15 Apr 2024 11:43:17 -0400
From: Peter Xu <peterx@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: syzbot <syzbot+ddf4b4c0005944105a9e@...kaller.appspotmail.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING in try_to_migrate_one (2)

On Thu, Apr 11, 2024 at 12:55:13PM -0700, Andrew Morton wrote:
> On Wed, 10 Apr 2024 19:04:21 -0700 syzbot <syzbot+ddf4b4c0005944105a9e@...kaller.appspotmail.com> wrote:
> 
> > syzbot has found a reproducer for the following issue on:
> 
> Thanks.
> 
> > HEAD commit:    480e035fc4c7 Merge tag 'drm-next-2024-03-13' of https://gi..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=14db82bd180000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=1e5b814e91787669
> > dashboard link: https://syzkaller.appspot.com/bug?extid=ddf4b4c0005944105a9e
> > 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=13111a4d180000
> 
> Seems to be userfaultfd related.
> 
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=156ae155180000

I can't easily trigger with the reproducer, neither did I get more
information from the syzbot reproducer, and it doesn't include an
UFFDIO_REGISTER.

Before go reading more on syzbot itself on this specific reproducer, I'll
see whether I can come up with something better than commit c2da319c2e2: I
don't remember the details why I didn't do the sanity check when updating
the pgtable rather than walking it.  I'll give it a shot this time.

Thanks,

-- 
Peter Xu