Re: [syzbot] [btrfs?] kernel BUG in scrub_handle_errored_block

[Qu Wenruo]

On 2023/4/23 07:46, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    af67688dca57 Merge tag 'mmc-v6.3-rc3' of git://git.kernel...
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=17f8020bc80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4afb87f3ec27b7fd
> dashboard link: https://syzkaller.appspot.com/bug?extid=e19c41a2f26eccf41aab
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/eaa3ac1127b4/disk-af67688d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/02dd376f6bb3/vmlinux-af67688d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/0162b8821f2f/bzImage-af67688d.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e19c41a2f26eccf41aab@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> BTRFS warning (device loop5): tree block 5423104 mirror 1 has bad bytenr, has 0 want 5423104
> assertion failed: 0, in fs/btrfs/scrub.c:614

This happens because we expect to got an block group during scrub.

I guess it's due to the concurrent balance and scrub runs, as most of 
the code would check if the block group is removed, but not in that call 
site.

Anyway the code is already removed in the incoming scrub rework, thus 
should not be a problem.

But I'm a little surprised that we even allow scrub and balance to run 
at the same time...

Thanks,
Qu
> ------------[ cut here ]------------
> kernel BUG at fs/btrfs/messages.c:259!
> invalid opcode: 0000 [#2] PREEMPT SMP KASAN
> CPU: 0 PID: 17944 Comm: kworker/u4:18 Tainted: G      D            6.3.0-rc7-syzkaller-00043-gaf67688dca57 #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
> Workqueue: btrfs-scrub scrub_bio_end_io_worker
> RIP: 0010:btrfs_assertfail+0x18/0x20 fs/btrfs/messages.c:259
> Code: df e8 2c 4c 43 f7 e9 50 fb ff ff e8 42 80 01 00 66 90 66 0f 1f 00 89 d1 48 89 f2 48 89 fe 48 c7 c7 80 ef 2b 8b e8 68 60 ff ff <0f> 0b 66 0f 1f 44 00 00 66 0f 1f 00 53 48 89 fb e8 a3 8b ed f6 48
> RSP: 0018:ffffc900166a7638 EFLAGS: 00010246
> RAX: 000000000000002c RBX: 0000000004248060 RCX: 8c5f616438692d00
> RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
> RBP: ffffc900166a7910 R08: ffffffff816df7fc R09: fffff52002cd4e41
> R10: 0000000000000000 R11: dffffc0000000001 R12: ffffc900166a7860
> R13: ffff888030d3d000 R14: dffffc0000000000 R15: ffff88801cd20000
> FS:  0000000000000000(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000001b33342000 CR3: 0000000029ac2000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   lock_full_stripe fs/btrfs/scrub.c:614 [inline]
>   scrub_handle_errored_block+0x1ee1/0x4730 fs/btrfs/scrub.c:1067
>   scrub_bio_end_io_worker+0x9bb/0x1370 fs/btrfs/scrub.c:2559
>   process_one_work+0x8a0/0x10e0 kernel/workqueue.c:2390
>   worker_thread+0xa63/0x1210 kernel/workqueue.c:2537
>   kthread+0x270/0x300 kernel/kthread.c:376
>   ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308
>   </TASK>
> Modules linked in:
>
>
> ---
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