WARNING: CPU: 0 PID: 1 at kernel/softirq.c:173 __local_bh_disable_ip+0xce/0xe0

I just hit this oops running impish:linux-realtime (5.13) inside a kvm instance. It looks like there's a locking issue between cgroups (idr allocator) and some real-time specific patches:

[ 5.278177] DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt))
[ 5.278184] WARNING: CPU: 0 PID: 1 at kernel/softirq.c:173 __local_bh_disable_ip+0xce/0xe0
[ 5.278189] Modules linked in: nls_utf8 isofs nls_iso8859_1 dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua ccp kvm input_leds joydev serio_raw mac_hid qemu_fw_cfg sch_fq_codel msr ip_tables x_tables autofs4 btrfs blake2b_generic zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear qxl drm_ttm_helper ttm drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops cec rc_core virtio_net psmouse virtio_blk i2c_i801 ahci net_failover xhci_pci failover xhci_pci_renesas drm libahci i2c_smbus lpc_ich
[ 5.278209] CPU: 0 PID: 1 Comm: systemd Not tainted 5.13.0-1001-realtime #1-Ubuntu
[ 5.278211] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
[ 5.278212] RIP: 0010:__local_bh_disable_ip+0xce/0xe0
[ 5.278213] Code: 76 ff ff ff e8 a3 bd 50 00 85 c0 74 a3 8b 05 11 92 0f 02 85 c0 75 99 48 c7 c6 88 29 3c 9e 48 c7 c7 02 cd 3a 9e e8 7b ee b4 00 <0f> 0b eb 82 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 0f 1f 44 00
[ 5.278214] RSP: 0018:ffffac46c0013d40 EFLAGS: 00010286
[ 5.278216] RAX: 0000000000000000 RBX: 0000000000000200 RCX: 0000000000000027
[ 5.278216] RDX: 0000000000000027 RSI: 40000000ffffe2df RDI: ffff9df4fbc18a58
[ 5.278217] RBP: ffffac46c0013d48 R08: ffff9df4fbc18a50 R09: 000000009f30a523
[ 5.278218] R10: ffffffffffffffff R11: 284e4f5f4e524157 R12: ffffffff9edd1e30
[ 5.278218] R13: 0000000000000000 R14: 0000000000000002 R15: 0000000000000000
[ 5.278219] FS: 00007f1d42909900(0000) GS:ffff9df4fbc00000(0000) knlGS:0000000000000000
[ 5.278220] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 5.278221] CR2: 0000561b36c201a0 CR3: 0000000102800000 CR4: 00000000000006f0
[ 5.278222] Call Trace:
[ 5.278224] cgroup_idr_alloc.constprop.0+0x38/0xd0
[ 5.278226] css_create+0x117/0x1e0
[ 5.278228] cgroup_apply_control_enable+0x13b/0x160
[ 5.278229] cgroup_mkdir+0xe2/0x1c0
[ 5.278230] kernfs_iop_mkdir+0x5c/0x90
[ 5.278232] vfs_mkdir+0x181/0x220
[ 5.278234] do_mkdirat+0x122/0x150
[ 5.278236] __x64_sys_mkdir+0x1b/0x20
[ 5.278237] do_syscall_64+0x61/0xb0
[ 5.278239] ? syscall_exit_to_user_mode+0x27/0x50
[ 5.278241] ? __x64_sys_mkdir+0x1b/0x20
[ 5.278242] ? do_syscall_64+0x6e/0xb0
[ 5.278243] ? do_syscall_64+0x6e/0xb0
[ 5.278244] ? asm_exc_page_fault+0x8/0x30
[ 5.278245] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 5.278246] RIP: 0033:0x7f1d430ca81b
[ 5.278247] Code: 8b 05 59 86 0d 00 41 bc ff ff ff ff 64 c7 00 16 00 00 00 e9 37 ff ff ff e8 c2 0c 02 00 66 90 f3 0f 1e fa b8 53 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 25 86 0d 00 f7 d8 64 89 01 48
[ 5.278248] RSP: 002b:00007fffaf9cdc78 EFLAGS: 00000202 ORIG_RAX: 0000000000000053
[ 5.278249] RAX: ffffffffffffffda RBX: 0000561b36d8d940 RCX: 00007f1d430ca81b
[ 5.278249] RDX: 0000000000000000 RSI: 00000000000001ed RDI: 0000561b36db9700
[ 5.278250] RBP: 00007f1d434ef52f R08: 0000000000000000 R09: 0000000000000000
[ 5.278250] R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
[ 5.278251] R13: 0000561b36d8d940 R14: 0000000000000001 R15: 0000000000000073
[ 5.278252] ---[ end trace 0000000000000002 ]---