Re: [syzbot] [btrfs?] kernel BUG in btrfs_exclop_balance (2)

[David Sterba]

On Fri, May 05, 2023 at 06:43:55PM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    7163a2111f6c Merge tag 'acpi-6.4-rc1-3' of git://git.kerne..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=175bb84c280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=73a06f6ef2d5b492
> dashboard link: https://syzkaller.appspot.com/bug?extid=5e466383663438b99b44
> compiler:       Debian clang version 15.0.7, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12048338280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11ff7314280000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/01051811f2fe/disk-7163a211.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/a26c68e4c8a6/vmlinux-7163a211.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/17380fb8dad4/bzImage-7163a211.xz
> mounted in repro: https://storage.googleapis.com/syzbot-assets/b30a249e8609/mount_0.gz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+5e466383663438b99b44@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> assertion failed: fs_info->exclusive_operation == BTRFS_EXCLOP_BALANCE_PAUSED, in fs/btrfs/ioctl.c:463

Looks like syzbot was able to hit another problem, the above assertion
is from a recent fix ac868bc9d136 ("btrfs: fix assertion of exclop
condition when starting balance").

> ------------[ cut here ]------------
> kernel BUG at fs/btrfs/messages.c:259!
> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 8630 Comm: syz-executor102 Not tainted 6.3.0-syzkaller-13225-g7163a2111f6c #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/14/2023
> RIP: 0010:btrfs_assertfail+0x18/0x20 fs/btrfs/messages.c:259
> Code: df e8 2c 05 36 f7 e9 50 fb ff ff e8 b2 90 01 00 66 90 66 0f 1f 00 89 d1 48 89 f2 48 89 fe 48 c7 c7 80 32 2c 8b e8 c8 60 ff ff <0f> 0b 66 0f 1f 44 00 00 66 0f 1f 00 53 48 89 fb e8 73 31 de f6 48
> RSP: 0018:ffffc9000ae27e48 EFLAGS: 00010246
> RAX: 0000000000000066 RBX: 1ffff1100fa13c18 RCX: e812ce05a9b3c300
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000002 R08: ffffffff816f0fec R09: fffff520015c4f7d
> R10: 0000000000000000 R11: dffffc0000000001 R12: ffff88807d09e0c0
> R13: ffff88807d09c000 R14: ffff88807d09c678 R15: dffffc0000000000
> FS:  00007f2bb10a8700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f2bb0c90000 CR3: 0000000028447000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  btrfs_exclop_balance+0x153/0x1f0 fs/btrfs/ioctl.c:463
>  btrfs_ioctl_balance+0x482/0x7c0 fs/btrfs/ioctl.c:3562
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:870 [inline]
>  __se_sys_ioctl+0xf1/0x160 fs/ioctl.c:856
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x7f2bb853ec69
> RSP: 002b:00007f2bb10a82f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f2bb85c87c0 RCX: 00007f2bb853ec69

If this could be relevant as some error code, RAX 0xda is -38 which is
ENOSYS, so there might be some combination of balance parameters that is
unexpected.

> RDX: 0000000020000540 RSI: 00000000c4009420 RDI: 0000000000000004
> RBP: 00007f2bb85951d0 R08: 00007f2bb10a8700 R09: 0000000000000000
> R10: 00007f2bb10a8700 R11: 0000000000000246 R12: 7fffffffffffffff
> R13: 0000000100000001 R14: 8000000000000001 R15: 00007f2bb85c87c8
>  </TASK>
> Modules linked in:
> ---[ end trace 0000000000000000 ]---
> RIP: 0010:btrfs_assertfail+0x18/0x20 fs/btrfs/messages.c:259
> RSP: 0018:ffffc9000ae27e48 EFLAGS: 00010246
> RAX: 0000000000000066 RBX: 1ffff1100fa13c18 RCX: e812ce05a9b3c300
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
> RBP: 0000000000000002 R08: ffffffff816f0fec R09: fffff520015c4f7d
> R10: 0000000000000000 R11: dffffc0000000001 R12: ffff88807d09e0c0
> R13: ffff88807d09c000 R14: ffff88807d09c678 R15: dffffc0000000000
> FS:  00007f2bb10a8700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f2bb0c90000 CR3: 0000000028447000 CR4: 00000000003506e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400