LTP ptrace01 test case triggers a warning below. Looks at ptrace_stop() calls cgroup_enter_frozen() there in the cgroup v2 freezer. [ 8373.336330] WARNING: CPU: 56 PID: 67026 at kernel/cgroup/cgroup.c:6008 cgroup_exit+0x2a9/0x2f0 [ 8373.345001] Modules linked in: brd ext4 crc16 mbcache jbd2 overlay loop nls_iso8859_1 nls_cp437 vfat fat kvm_amd kvm ses enclosure dax_pmem irqbypass dax_pmem_core efivars ip_tables x_tables xfs sd_mod smartpqi scsi_transport_sas tg3 mlx5_core libphy firmware_class dm_mirror dm_region_hash dm_log dm_mod efivarfs [last unloaded: dummy_del_mod] [ 8373.375561] CPU: 56 PID: 67026 Comm: ptrace01 Tainted: G O 5.1.0-next-20190507+ #25 [ 8373.384579] Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 01/25/2019 [ 8373.393164] RIP: 0010:cgroup_exit+0x2a9/0x2f0 [ 8373.397556] Code: 0d ff ff ff 4c 89 f7 e8 75 4b 1b 00 4c 8b ab 20 0f 00 00 49 8d 7d 50 e8 65 4b 1b 00 49 8b 7d 50 e8 4c 56 00 00 e9 db fe ff ff <0f> 0b e9 3a fe ff ff 48 01 f1 0f 82 3b ff ff ff 48 c7 c7 40 83 5b [ 8373.416443] RSP: 0018:ffff888bdc9ef9b8 EFLAGS: 00010002 [ 8373.421709] RAX: 0000000000000000 RBX: ffff888e5cfcc040 RCX: ffffffffab3a8e7d [ 8373.428897] RDX: 1ffff111cb9f9875 RSI: dffffc0000000000 RDI: ffff888e5cfcc3a8 [ 8373.436080] RBP: ffff888bdc9efa50 R08: ffffed117b93df25 R09: ffffed117b93df24 [ 8373.443266] R10: ffffed117b93df24 R11: 0000000000000003 R12: ffff888bdc9efa28 [ 8373.450451] R13: ffff888f4c2346c8 R14: ffff888e5cfccf60 R15: ffff888e5cfccf68 [ 8373.457637] FS: 00007ff1e2e3d5c0(0000) GS:ffff88902f800000(0000) knlGS:0000000000000000 [ 8373.465781] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 8373.471569] CR2: 00007ff1e286fe8a CR3: 000000092c412000 CR4: 00000000001406a0 [ 8373.478750] Call Trace: [ 8373.481219] ? cgroup_post_fork+0x350/0x350 [ 8373.485435] ? fpu__drop+0x5e/0x230 [ 8373.488951] ? exit_thread+0x10c/0x160 [ 8373.492736] do_exit+0x5cb/0x1740 [ 8373.496083] ? check_chain_key+0x142/0x200 [ 8373.500210] ? mm_update_next_owner+0x360/0x360 [ 8373.504775] ? map_id_up+0x14c/0x1f0 [ 8373.508380] ? check_chain_key+0x142/0x200 [ 8373.512512] ? get_signal+0x5f1/0xde0 [ 8373.516206] ? lock_downgrade+0x300/0x300 [ 8373.520246] ? lock_downgrade+0x300/0x300 [ 8373.524287] do_group_exit+0x78/0x160 [ 8373.527978] get_signal+0x1e8/0xde0 [ 8373.531498] do_signal+0x9c/0x9d0 [ 8373.534841] ? check_chain_key+0x142/0x200 [ 8373.538970] ? setup_sigcontext+0x280/0x280 [ 8373.543185] ? lock_downgrade+0x300/0x300 [ 8373.547228] ? kill_pid_info+0x2e/0xd0 [ 8373.551006] ? kill_pid_info+0xa4/0xd0 [ 8373.554788] ? __x64_sys_kill+0x262/0x350 [ 8373.558830] exit_to_usermode_loop+0x9d/0xc0 [ 8373.563131] do_syscall_64+0x470/0x5d8 [ 8373.566910] ? syscall_return_slowpath+0xf0/0xf0 [ 8373.571565] ? __do_page_fault+0x44d/0x5b0 [ 8373.575698] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 8373.580789] RIP: 0033:0x7ff1e2893c3b [ 8373.584402] Code: Bad RIP value. [ 8373.587653] RSP: 002b:00007ffd8e5efe78 EFLAGS: 00000206 ORIG_RAX: 000000000000003e [ 8373.595276] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007ff1e2893c3b [ 8373.602461] RDX: 0000000000000000 RSI: 000000000000000c RDI: 00000000000105d2 [ 8373.609642] RBP: 0000000000000000 R08: 00000000ffffffff R09: 00007ff1e2e3d5c0 [ 8373.616824] R10: fffffffffffff768 R11: 0000000000000206 R12: 00007ffd8e5efe98 [ 8373.624005] R13: 00007ffd8e5f00c0 R14: 0000000000000000 R15: 0000000000000000 [ 8373.631190] ---[ end trace a7169f3366f1d100 ]---
