With the enhanced CPU hotplug lockdep coverage the following lockdep splat happens: ====================================================== WARNING: possible circular locking dependency detected 4.12.0-rc2+ #84 Tainted: G W ------------------------------------------------------ cpuhp/1/15 is trying to acquire lock: flush_work+0x39/0x2f0 but task is already holding lock: cpuhp_thread_fun+0x30/0x160 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (cpuhp_state){+.+.+.}: lock_acquire+0xb4/0x200 cpuhp_kick_ap_work+0x72/0x330 _cpu_down+0x8b/0x100 do_cpu_down+0x3e/0x60 cpu_down+0x10/0x20 cpu_subsys_offline+0x14/0x20 device_offline+0x88/0xb0 online_store+0x4c/0xa0 dev_attr_store+0x18/0x30 sysfs_kf_write+0x45/0x60 kernfs_fop_write+0x156/0x1e0 __vfs_write+0x37/0x160 vfs_write+0xca/0x1c0 SyS_write+0x58/0xc0 entry_SYSCALL_64_fastpath+0x23/0xc2 -> #1 (cpu_hotplug_lock.rw_sem){++++++}: lock_acquire+0xb4/0x200 cpus_read_lock+0x3d/0xb0 apply_workqueue_attrs+0x17/0x50 __alloc_workqueue_key+0x1e1/0x530 scsi_host_alloc+0x373/0x480 [scsi_mod] ata_scsi_add_hosts+0xcb/0x130 [libata] ata_host_register+0x11a/0x2c0 [libata] ata_host_activate+0xf0/0x150 [libata] ahci_host_activate+0x13e/0x170 [libahci] ahci_init_one+0xa3a/0xd3f [ahci] local_pci_probe+0x45/0xa0 work_for_cpu_fn+0x14/0x20 process_one_work+0x1f9/0x690 worker_thread+0x200/0x3d0 kthread+0x138/0x170 ret_from_fork+0x31/0x40 -> #0 ((&wfc.work)){+.+.+.}: __lock_acquire+0x11e1/0x13e0 lock_acquire+0xb4/0x200 flush_work+0x5c/0x2f0 work_on_cpu+0xa1/0xd0 acpi_processor_get_throttling+0x3d/0x50 acpi_processor_reevaluate_tstate+0x2c/0x50 acpi_soft_cpu_online+0x69/0xd0 cpuhp_invoke_callback+0xb4/0x8b0 cpuhp_up_callbacks+0x36/0xc0 cpuhp_thread_fun+0x14e/0x160 smpboot_thread_fn+0x1e8/0x300 kthread+0x138/0x170 ret_from_fork+0x31/0x40 other info that might help us debug this: Chain exists of: (&wfc.work) --> cpu_hotplug_lock.rw_sem --> cpuhp_state Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(cpuhp_state); lock(cpu_hotplug_lock.rw_sem); lock(cpuhp_state); lock((&wfc.work)); *** DEADLOCK *** 1 lock held by cpuhp/1/15: cpuhp_thread_fun+0x30/0x160 stack backtrace: CPU: 1 PID: 15 Comm: cpuhp/1 Tainted: G W 4.12.0-rc2+ #84 Hardware name: Supermicro SYS-4048B-TR4FT/X10QBi, BIOS 1.1a 07/29/2015 Call Trace: dump_stack+0x85/0xc4 print_circular_bug+0x209/0x217 __lock_acquire+0x11e1/0x13e0 lock_acquire+0xb4/0x200 ? lock_acquire+0xb4/0x200 ? flush_work+0x39/0x2f0 ? acpi_processor_start+0x50/0x50 flush_work+0x5c/0x2f0 ? flush_work+0x39/0x2f0 ? acpi_processor_start+0x50/0x50 ? mark_held_locks+0x6d/0x90 ? queue_work_on+0x56/0x90 ? trace_hardirqs_on_caller+0x154/0x1c0 ? trace_hardirqs_on+0xd/0x10 ? acpi_processor_start+0x50/0x50 work_on_cpu+0xa1/0xd0 ? find_worker_executing_work+0x50/0x50 ? acpi_processor_power_exit+0x70/0x70 acpi_processor_get_throttling+0x3d/0x50 acpi_processor_reevaluate_tstate+0x2c/0x50 acpi_soft_cpu_online+0x69/0xd0 cpuhp_invoke_callback+0xb4/0x8b0 ? lock_acquire+0xb4/0x200 ? padata_replace+0x120/0x120 cpuhp_up_callbacks+0x36/0xc0 cpuhp_thread_fun+0x14e/0x160 smpboot_thread_fn+0x1e8/0x300 kthread+0x138/0x170 ? sort_range+0x30/0x30 ? kthread_create_on_node+0x70/0x70 ret_from_fork+0x31/0x40 The problem is that the work is scheduled on the current CPU from the hotplug thread associated with that CPU. It's not required to invoke these functions via the workqueue because the hotplug thread runs on the target CPU already. Check whether current is a per cpu thread pinned on the target CPU and invoke the function directly to avoid the workqueue. Signed-off-by: Thomas Gleixner Cc: "Rafael J. Wysocki" Cc: Len Brown Cc: linux-acpi@vger.kernel.org --- drivers/acpi/processor_throttling.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) --- a/drivers/acpi/processor_throttling.c +++ b/drivers/acpi/processor_throttling.c @@ -909,6 +909,13 @@ static long __acpi_processor_get_throttl return pr->throttling.acpi_processor_get_throttling(pr); } +static int call_on_cpu(int cpu, long (*fn)(void *), void *arg, bool direct) +{ + if (direct || (is_percpu_thread() && cpu == smp_processor_id())) + return fn(arg); + return work_on_cpu(cpu, fn, arg); +} + static int acpi_processor_get_throttling(struct acpi_processor *pr) { if (!pr) @@ -926,7 +933,7 @@ static int acpi_processor_get_throttling if (!cpu_online(pr->id)) return -ENODEV; - return work_on_cpu(pr->id, __acpi_processor_get_throttling, pr); + return call_on_cpu(pr->id, __acpi_processor_get_throttling, pr, false); } static int acpi_processor_get_fadt_info(struct acpi_processor *pr) @@ -1076,13 +1083,6 @@ static long acpi_processor_throttling_fn arg->target_state, arg->force); } -static int call_on_cpu(int cpu, long (*fn)(void *), void *arg, bool direct) -{ - if (direct) - return fn(arg); - return work_on_cpu(cpu, fn, arg); -} - static int __acpi_processor_set_throttling(struct acpi_processor *pr, int state, bool force, bool direct) {