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

[Qu Wenruo]

On 2023/8/1 22:58, syzbot wrote:
> Hello,
>
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> WARNING in prepare_to_merge
>
> BTRFS error (device loop3): reloc tree mismatch, root 8 has no reloc root, expect reloc root key (-8, 132, 8) gen 17

#syz test: https://github.com/adam900710/linux graceful_reloc_mismatch

I have added another patch to reject those invalid reloc tree keys, thus
at least we could have a more graceful rejection (without kernel warnings).

But the previous patch is still needed to catch not-so-obvious corrupted
reloc root keys.

Thanks,
Qu
> ------------[ cut here ]------------
> BTRFS: Transaction aborted (error -117)
> WARNING: CPU: 1 PID: 10413 at fs/btrfs/relocation.c:1946 prepare_to_merge+0x10e0/0x1460 fs/btrfs/relocation.c:1946
> Modules linked in:
> CPU: 1 PID: 10413 Comm: syz-executor.3 Not tainted 6.5.0-rc3-syzkaller-g9f2c8c9193cc #0
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> RIP: 0010:prepare_to_merge+0x10e0/0x1460 fs/btrfs/relocation.c:1946
> Code: 8b 7e 50 44 89 e2 48 c7 c6 20 d8 b6 8a e8 58 1b 10 00 eb c1 e8 d1 83 00 fe be 8b ff ff ff 48 c7 c7 80 d7 b6 8a e8 f0 4b c7 fd <0f> 0b e9 bf fe ff ff 48 8b 7c 24 28 e8 af 93 53 fe e9 3e f5 ff ff
> RSP: 0018:ffffc90003ebf6b0 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffff8880478f2b78 RCX: 0000000000000000
> RDX: ffff8880466c9300 RSI: ffffffff814c5346 RDI: 0000000000000001
> RBP: 0000000000000001 R08: 0000000000000001 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000046525442 R12: 0000000000000000
> R13: 0000000000000084 R14: ffff8880478f2b28 R15: ffff888030e28000
> FS:  00007fcc9098a6c0(0000) GS:ffff88806b700000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fcc90968f28 CR3: 000000001fa0c000 CR4: 0000000000350ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   <TASK>
>   relocate_block_group+0x8d1/0xe70 fs/btrfs/relocation.c:3782
>   btrfs_relocate_block_group+0x714/0xd90 fs/btrfs/relocation.c:4120
>   btrfs_relocate_chunk+0x143/0x440 fs/btrfs/volumes.c:3277
>   __btrfs_balance fs/btrfs/volumes.c:4012 [inline]
>   btrfs_balance+0x20fc/0x3ef0 fs/btrfs/volumes.c:4389
>   btrfs_ioctl_balance fs/btrfs/ioctl.c:3604 [inline]
>   btrfs_ioctl+0x1362/0x5cf0 fs/btrfs/ioctl.c:4637
>   vfs_ioctl fs/ioctl.c:51 [inline]
>   __do_sys_ioctl fs/ioctl.c:870 [inline]
>   __se_sys_ioctl fs/ioctl.c:856 [inline]
>   __x64_sys_ioctl+0x18f/0x210 fs/ioctl.c:856
>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>   do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:80
>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7fcc8fc7cae9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fcc9098a0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007fcc8fd9bf80 RCX: 00007fcc8fc7cae9
> RDX: 00000000200003c0 RSI: 00000000c4009420 RDI: 0000000000000005
> RBP: 00007fcc8fcc847a R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007fcc8fd9bf80 R15: 00007ffd6ad55508
>   </TASK>
>
>
> Tested on:
>
> commit:         9f2c8c91 btrfs: exit gracefully if reloc roots don't m..
> git tree:       https://github.com/adam900710/linux graceful_reloc_mismatch
> console output: https://syzkaller.appspot.com/x/log.txt?x=173afb31a80000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=23c579cf0ae1addd
> dashboard link: https://syzkaller.appspot.com/bug?extid=ae97a827ae1c3336bbb4
> compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>
> Note: no patches were applied.