[<0>] rwsem_down_write_slowpath+0x329/0x4e0
[<0>] btrfs_delete_subvolume+0x90/0x5f0 [btrfs]
[<0>] btrfs_ioctl_snap_destroy+0x5b3/0x6f0 [btrfs]
[<0>] btrfs_ioctl+0xa5f/0x2ef0 [btrfs]
[<0>] ksys_ioctl+0x86/0xc0
[<0>] __x64_sys_ioctl+0x16/0x20
[<0>] do_syscall_64+0x52/0x170
[<0>] entry_SYSCALL_64_after_hwframe+0x44/0xa9