Re: WARNING in close_fs_devices (2)

[Anand Jain]

On 18/9/20 7:22 pm, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    e4c26faa Merge tag 'usb-5.9-rc5' of git://git.kernel.org/p..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15bf1621900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c61610091f4ca8c4
> dashboard link: https://syzkaller.appspot.com/bug?extid=4cfe71a4da060be47502
> compiler:       gcc (GCC) 10.1.0-syz 20200507
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+4cfe71a4da060be47502@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 3612 at fs/btrfs/volumes.c:1166 close_fs_devices.part.0+0x607/0x800 fs/btrfs/volumes.c:1166
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 3612 Comm: syz-executor.2 Not tainted 5.9.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:77 [inline]
>   dump_stack+0x198/0x1fd lib/dump_stack.c:118
>   panic+0x347/0x7c0 kernel/panic.c:231
>   __warn.cold+0x20/0x46 kernel/panic.c:600
>   report_bug+0x1bd/0x210 lib/bug.c:198
>   handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
>   exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
>   asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
> RIP: 0010:close_fs_devices.part.0+0x607/0x800 fs/btrfs/volumes.c:1166
> Code: 0f b6 04 02 84 c0 74 02 7e 33 48 8b 44 24 18 c6 80 30 01 00 00 00 48 83 c4 30 5b 5d 41 5c 41 5d 41 5e 41 5f c3 e8 99 ce 6a fe <0f> 0b e9 71 ff ff ff e8 8d ce 6a fe 0f 0b e9 20 ff ff ff e8 d1 d5
> RSP: 0018:ffffc900091777e0 EFLAGS: 00010246
> RAX: 0000000000040000 RBX: ffffffffffffffff RCX: ffffc9000c8b7000
> RDX: 0000000000040000 RSI: ffffffff83097f47 RDI: 0000000000000007
> RBP: dffffc0000000000 R08: 0000000000000001 R09: ffff8880988a187f
> R10: 0000000000000000 R11: 0000000000000001 R12: ffff88809593a130
> R13: ffff88809593a1ec R14: ffff8880988a1908 R15: ffff88809593a050
>   close_fs_devices fs/btrfs/volumes.c:1193 [inline]
>   btrfs_close_devices+0x95/0x1f0 fs/btrfs/volumes.c:1179
>   open_ctree+0x4984/0x4a2d fs/btrfs/disk-io.c:3434
>   btrfs_fill_super fs/btrfs/super.c:1316 [inline]
>   btrfs_mount_root.cold+0x14/0x165 fs/btrfs/super.c:1672
>   legacy_get_tree+0x105/0x220 fs/fs_context.c:592
>   vfs_get_tree+0x89/0x2f0 fs/super.c:1547
>   fc_mount fs/namespace.c:978 [inline]
>   vfs_kern_mount.part.0+0xd3/0x170 fs/namespace.c:1008
>   vfs_kern_mount+0x3c/0x60 fs/namespace.c:995
>   btrfs_mount+0x234/0xaa0 fs/btrfs/super.c:1732
>   legacy_get_tree+0x105/0x220 fs/fs_context.c:592
>   vfs_get_tree+0x89/0x2f0 fs/super.c:1547
>   do_new_mount fs/namespace.c:2875 [inline]
>   path_mount+0x1387/0x2070 fs/namespace.c:3192
>   do_mount fs/namespace.c:3205 [inline]
>   __do_sys_mount fs/namespace.c:3413 [inline]
>   __se_sys_mount fs/namespace.c:3390 [inline]
>   __x64_sys_mount+0x27f/0x300 fs/namespace.c:3390
>   do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x46004a
> Code: b8 a6 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 fd 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 da 89 fb ff c3 66 0f 1f 84 00 00 00 00 00
> RSP: 002b:00007f414d78da88 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00007f414d78db20 RCX: 000000000046004a
> RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007f414d78dae0
> RBP: 00007f414d78dae0 R08: 00007f414d78db20 R09: 0000000020000000
> R10: 0000000000000000 R11: 0000000000000202 R12: 0000000020000000
> R13: 0000000020000100 R14: 0000000020000200 R15: 000000002001a800
> Kernel Offset: disabled
> Rebooting in 86400 seconds..


#syz fix: btrfs: fix rw_devices count in __btrfs_free_extra_devids