linux-kernel - Re: [syzbot] [maple-tree?] BUG: unable to handle kernel paging request in mas

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Date: Tue, 4 Jun 2024 09:41:47 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: syzbot <syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, maple-tree@...ts.infradead.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [maple-tree?] BUG: unable to handle kernel paging
 request in mas_walk

* syzbot <syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com> [240603 22:23]:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    4a4be1ad3a6e Revert "vfs: Delete the associated dentry whe..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=128638ba980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=bd6024aedb15e15c
> dashboard link: https://syzkaller.appspot.com/bug?extid=c67d06ab25a9bc4adf35
> compiler:       aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=106f71aa980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b4ffc6980000
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-4a4be1ad.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/75957361122b/vmlinux-4a4be1ad.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/6c766b0ec377/Image-4a4be1ad.gz.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+c67d06ab25a9bc4adf35@...kaller.appspotmail.com
> 
> Unable to handle kernel paging request at virtual address 00700000077b9b78

Never a good thing.

I'm looking into this but it's not easily recreated because I keep
hitting another but with the reproducer [1].  I tried the HEAD commit
and the more recent v6.10-rc2.

I have a decent idea of what is going on here, but need to prove the
fix.

[1] https://syzkaller.appspot.com/bug?extid=7eaa0d7b9fccf21052f1

Thanks,
Liam