linux-kernel - Re: [syzbot] [bcachefs?] kernel BUG in bch2_bucket_alloc

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Date: Sun, 23 Jun 2024 16:56:59 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: syzbot <syzbot+3d2944b5612507034fc4@...kaller.appspotmail.com>
Cc: bfoster@...hat.com, linux-bcachefs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] kernel BUG in bch2_bucket_alloc_freelist

On Sun, Jun 23, 2024 at 02:23:21AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    2ccbdf43d5e7 Merge tag 'for-linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15b13146980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=81c0d76ceef02b39
> dashboard link: https://syzkaller.appspot.com/bug?extid=3d2944b5612507034fc4
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: i386
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7bc7510fe41f/non_bootable_disk-2ccbdf43.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/13cdb5bfbafa/vmlinux-2ccbdf43.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/7a14f5d07f81/bzImage-2ccbdf43.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+3d2944b5612507034fc4@...kaller.appspotmail.com
> 
> ------------[ cut here ]------------
> kernel BUG at fs/bcachefs/alloc_foreground.c:489!

So it turns out, this one is from onlining a device (already a member of
the filesystem) that doesn't have a journal allocated; we end up using
bch2_bucket_alloc_new_fs() when we're not supposed to.

I started a rework of the early filesystem bringup allocation paths
awhile ago to get rid of that entirely, perhaps I shall finish that.