Hi, I observed following warning from lockdep triggerd by 'slabinfo -d' right after boot. There is nothing funky running in background, it's a minimal rootfs created with buildroot. Kernel version: v5.5.0-rc1 Kernel config for x86_64: defconfig + kvmconfig + lockdep + debug locks # slabinfo -d Acpi-Namespace not empty cannot disable sanity checks Acpi-Namespace not empty cannot disable redzoning Acpi-Operand not empty cannot disable sanity checks Acpi-Operand not empty cannot disable redzoning [ 5.033027] [ 5.033173] ====================================================== [ 5.033712] WARNING: possible circular locking dependency detected [ 5.034250] 5.5.0-rc1 #11 Not tainted [ 5.034572] ------------------------------------------------------ [ 5.035108] slabinfo/136 is trying to acquire lock: [ 5.035541] ffffffff8265eff0 (cpu_hotplug_lock.rw_sem){++++}, at: kmem_cache_shrink_all+0x9/0x20 [ 5.036313] [ 5.036313] but task is already holding lock: [ 5.036833] ffff88803cec63f8 (kn->count#39){++++}, at: kernfs_fop_write+0x9b/0x1b0 [ 5.037500] [ 5.037500] which lock already depends on the new lock. [ 5.037500] [ 5.038208] [ 5.038208] the existing dependency chain (in reverse order) is: [ 5.038862] [ 5.038862] -> #2 (kn->count#39){++++}: [ 5.039329] __kernfs_remove+0x240/0x2e0 [ 5.039717] kernfs_remove_by_name_ns+0x3c/0x80 [ 5.040159] sysfs_slab_add+0x184/0x250 [ 5.040551] __kmem_cache_create+0x37c/0x410 [ 5.040969] kmem_cache_create_usercopy+0x150/0x270 [ 5.041442] kmem_cache_create+0xd/0x10 [ 5.041831] i915_global_scheduler_init+0x1e/0x7c [ 5.042289] i915_globals_init+0xf/0x95 [ 5.042668] i915_init+0x8/0x5d [ 5.042988] do_one_initcall+0x58/0x29f [ 5.043375] kernel_init_freeable+0x1ae/0x238 [ 5.043804] kernel_init+0x5/0xf7 [ 5.044139] ret_from_fork+0x27/0x50 [ 5.044499] [ 5.044499] -> #1 (slab_mutex){+.+.}: [ 5.044950] __mutex_lock+0x86/0x900 [ 5.045310] kmem_cache_create_usercopy+0x32/0x270 [ 5.045768] kmem_cache_create+0xd/0x10 [ 5.046146] ptlock_cache_init+0x1b/0x23 [ 5.046534] start_kernel+0x21f/0x4f4 [ 5.046898] secondary_startup_64+0xb6/0xc0 [ 5.047309] [ 5.047309] -> #0 (cpu_hotplug_lock.rw_sem){++++}: [ 5.047849] __lock_acquire+0xe2f/0x19f0 [ 5.048233] lock_acquire+0x95/0x180 [ 5.048604] cpus_read_lock+0x26/0x90 [ 5.048970] kmem_cache_shrink_all+0x9/0x20 [ 5.049386] shrink_store+0xe/0x20 [ 5.049730] slab_attr_store+0x1b/0x30 [ 5.050103] kernfs_fop_write+0xca/0x1b0 [ 5.050494] vfs_write+0xb4/0x1a0 [ 5.050830] ksys_write+0x63/0xe0 [ 5.051165] do_syscall_64+0x4b/0x1e0 [ 5.051533] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 5.052012] [ 5.052012] other info that might help us debug this: [ 5.052012] [ 5.052707] Chain exists of: [ 5.052707] cpu_hotplug_lock.rw_sem --> slab_mutex --> kn->count#39 [ 5.052707] [ 5.053629] Possible unsafe locking scenario: [ 5.053629] [ 5.054137] CPU0 CPU1 [ 5.054529] ---- ---- [ 5.054922] lock(kn->count#39); [ 5.055211] lock(slab_mutex); [ 5.055695] lock(kn->count#39); [ 5.056195] lock(cpu_hotplug_lock.rw_sem); [ 5.056580] [ 5.056580] *** DEADLOCK *** [ 5.056580] [ 5.057087] 3 locks held by slabinfo/136: [ 5.057439] #0: ffff88803c151480 (sb_writers#7){.+.+}, at: vfs_write+0x13b/0x1a0 [ 5.058078] #1: ffff88803c1a7890 (&of->mutex){+.+.}, at: kernfs_fop_write+0x93/0x1b0 [ 5.058745] #2: ffff88803cec63f8 (kn->count#39){++++}, at: kernfs_fop_write+0x9b/0x1b0 [ 5.059426] [ 5.059426] stack backtrace: [ 5.059803] CPU: 0 PID: 136 Comm: slabinfo Not tainted 5.5.0-rc1 #11 [ 5.060349] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 [ 5.061320] Call Trace: [ 5.061538] dump_stack+0x71/0xa0 [ 5.061829] check_noncircular+0x176/0x190 [ 5.062193] __lock_acquire+0xe2f/0x19f0 [ 5.062542] lock_acquire+0x95/0x180 [ 5.062856] ? kmem_cache_shrink_all+0x9/0x20 [ 5.063236] cpus_read_lock+0x26/0x90 [ 5.063555] ? kmem_cache_shrink_all+0x9/0x20 [ 5.063931] kmem_cache_shrink_all+0x9/0x20 [ 5.064296] shrink_store+0xe/0x20 [ 5.064604] slab_attr_store+0x1b/0x30 [ 5.064931] kernfs_fop_write+0xca/0x1b0 [ 5.065273] vfs_write+0xb4/0x1a0 [ 5.065564] ksys_write+0x63/0xe0 [ 5.065855] do_syscall_64+0x4b/0x1e0 [ 5.066175] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 5.066610] RIP: 0033:0x45c283 [ 5.066877] Code: ff ff f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb bb 0f 1f 80 00 00 00 00 64 8b 04 25 18 00 00 00 85 c0 75 14 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 55 c3 0f 1f 40 00 48 83 ec 28 48 89 54 24 18 [ 5.068456] RSP: 002b:00007ffd3d486908 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 5.069106] RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 000000000045c283 [ 5.069728] RDX: 0000000000000002 RSI: 0000000002342360 RDI: 0000000000000003 [ 5.070347] RBP: 0000000002342360 R08: 0000000000000000 R09: 0000000000000002 [ 5.070964] R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000002 [ 5.071574] R13: 000000000234a3a0 R14: 0000000000000002 R15: 00000000004c6ec0 Cannot write to Acpi-Parse/sanity Thanks, Daniel