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SubjectRe: [PATCH v2] x86/acpi: fix a deadlock with cpu hotplug
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> On Apr 3, 2020, at 9:43 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>
> On Friday, April 3, 2020 1:18:07 PM CEST Qian Cai wrote:
>>
>>> On Apr 3, 2020, at 5:29 AM, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
>>>
>>> On Sunday, March 29, 2020 4:21:09 PM CEST Qian Cai wrote:
>>>> Similar to the commit 0266d81e9bf5 ("acpi/processor: Prevent cpu hotplug
>>>> deadlock") except this is for acpi_processor_ffh_cstate_probe():
>>>>
>>>> "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."
>>>>
>>>> Since CONFIG_ACPI_PROCESSOR (for cstate.c) selects
>>>> CONFIG_ACPI_CPU_FREQ_PSS (for processor_throttling.c) on x86, just
>>>> make call_on_cpu() a static inline function from processor_throttling.c
>>>> and use it in cstate.c.
>>>>
>>>> WARNING: possible circular locking dependency detected
>>>> ------------------------------------------------------
>>>> cpuhp/1/15 is trying to acquire lock:
>>>> ffffc90003447a28 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: __flush_work+0x4c6/0x630
>>>>
>>>> but task is already holding lock:
>>>> ffffffffafa1c0e8 (cpuidle_lock){+.+.}-{3:3}, at: cpuidle_pause_and_lock+0x17/0x20
>>>>
>>>> which lock already depends on the new lock.
>>>>
>>>> the existing dependency chain (in reverse order) is:
>>>>
>>>> -> #1 (cpu_hotplug_lock){++++}-{0:0}:
>>>> cpus_read_lock+0x3e/0xc0
>>>> irq_calc_affinity_vectors+0x5f/0x91
>>>> __pci_enable_msix_range+0x10f/0x9a0
>>>> pci_alloc_irq_vectors_affinity+0x13e/0x1f0
>>>> pci_alloc_irq_vectors_affinity at drivers/pci/msi.c:1208
>>>> pqi_ctrl_init+0x72f/0x1618 [smartpqi]
>>>> pqi_pci_probe.cold.63+0x882/0x892 [smartpqi]
>>>> local_pci_probe+0x7a/0xc0
>>>> work_for_cpu_fn+0x2e/0x50
>>>> process_one_work+0x57e/0xb90
>>>> worker_thread+0x363/0x5b0
>>>> kthread+0x1f4/0x220
>>>> ret_from_fork+0x27/0x50
>>>>
>>>> -> #0 ((work_completion)(&wfc.work)){+.+.}-{0:0}:
>>>> __lock_acquire+0x2244/0x32a0
>>>> lock_acquire+0x1a2/0x680
>>>> __flush_work+0x4e6/0x630
>>>> work_on_cpu+0x114/0x160
>>>> acpi_processor_ffh_cstate_probe+0x129/0x250
>>>> acpi_processor_evaluate_cst+0x4c8/0x580
>>>> acpi_processor_get_power_info+0x86/0x740
>>>> acpi_processor_hotplug+0xc3/0x140
>>>> acpi_soft_cpu_online+0x102/0x1d0
>>>> cpuhp_invoke_callback+0x197/0x1120
>>>> cpuhp_thread_fun+0x252/0x2f0
>>>> smpboot_thread_fn+0x255/0x440
>>>> kthread+0x1f4/0x220
>>>> ret_from_fork+0x27/0x50
>>>>
>>>> other info that might help us debug this:
>>>>
>>>> Chain exists of:
>>>> (work_completion)(&wfc.work) --> cpuhp_state-up --> cpuidle_lock
>>>>
>>>> Possible unsafe locking scenario:
>>>>
>>>> CPU0 CPU1
>>>> ---- ----
>>>> lock(cpuidle_lock);
>>>> lock(cpuhp_state-up);
>>>> lock(cpuidle_lock);
>>>> lock((work_completion)(&wfc.work));
>>>>
>>>> *** DEADLOCK ***
>>>>
>>>> 3 locks held by cpuhp/1/15:
>>>> #0: ffffffffaf51ab10 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x69/0x2f0
>>>> #1: ffffffffaf51ad40 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x69/0x2f0
>>>> #2: ffffffffafa1c0e8 (cpuidle_lock){+.+.}-{3:3}, at: cpuidle_pause_and_lock+0x17/0x20
>>>>
>>>> Call Trace:
>>>> dump_stack+0xa0/0xea
>>>> print_circular_bug.cold.52+0x147/0x14c
>>>> check_noncircular+0x295/0x2d0
>>>> __lock_acquire+0x2244/0x32a0
>>>> lock_acquire+0x1a2/0x680
>>>> __flush_work+0x4e6/0x630
>>>> work_on_cpu+0x114/0x160
>>>> acpi_processor_ffh_cstate_probe+0x129/0x250
>>>> acpi_processor_evaluate_cst+0x4c8/0x580
>>>> acpi_processor_get_power_info+0x86/0x740
>>>> acpi_processor_hotplug+0xc3/0x140
>>>> acpi_soft_cpu_online+0x102/0x1d0
>>>> cpuhp_invoke_callback+0x197/0x1120
>>>> cpuhp_thread_fun+0x252/0x2f0
>>>> smpboot_thread_fn+0x255/0x440
>>>> kthread+0x1f4/0x220
>>>> ret_from_fork+0x27/0x50
>>>>
>>>> Signed-off-by: Qian Cai <cai@lca.pw>
>>>> ---
>>>>
>>>> v2:
>>>> Make call_on_cpu() a static inline function to avoid a compilation
>>>> error when ACPI_PROCESSOR=m thanks to lkp@intel.com.
>>>>
>>>> arch/x86/kernel/acpi/cstate.c | 3 ++-
>>>> drivers/acpi/processor_throttling.c | 7 -------
>>>> include/acpi/processor.h | 10 ++++++++++
>>>> 3 files changed, 12 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
>>>> index caf2edccbad2..49ae4e1ac9cd 100644
>>>> --- a/arch/x86/kernel/acpi/cstate.c
>>>> +++ b/arch/x86/kernel/acpi/cstate.c
>>>> @@ -161,7 +161,8 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
>>>>
>>>> /* Make sure we are running on right CPU */
>>>>
>>>> - retval = work_on_cpu(cpu, acpi_processor_ffh_cstate_probe_cpu, cx);
>>>> + retval = call_on_cpu(cpu, acpi_processor_ffh_cstate_probe_cpu, cx,
>>>> + false);
>>>> if (retval == 0) {
>>>> /* Use the hint in CST */
>>>> percpu_entry->states[cx->index].eax = cx->address;
>>>> diff --git a/drivers/acpi/processor_throttling.c b/drivers/acpi/processor_throttling.c
>>>> index 532a1ae3595a..a0bd56ece3ff 100644
>>>> --- a/drivers/acpi/processor_throttling.c
>>>> +++ b/drivers/acpi/processor_throttling.c
>>>> @@ -897,13 +897,6 @@ static long __acpi_processor_get_throttling(void *data)
>>>> 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)
>>>> diff --git a/include/acpi/processor.h b/include/acpi/processor.h
>>>> index 47805172e73d..770d226b22f2 100644
>>>> --- a/include/acpi/processor.h
>>>> +++ b/include/acpi/processor.h
>>>> @@ -297,6 +297,16 @@ static inline void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx
>>>> }
>>>> #endif
>>>>
>>>> +#ifdef CONFIG_ACPI_CPU_FREQ_PSS
>>>
>>> Why does this depend on CONFIG_ACPI_CPU_FREQ_PSS?
>>
>> call_on_cpu() was only used in processor_throttling.c which has,
>>
>> processor-$(CONFIG_ACPI_CPU_FREQ_PSS) += processor_throttling.o
>>
>> after this patch, it will also be used in cstate.c which has,
>>
>> ifneq ($(CONFIG_ACPI_PROCESSOR),)
>> obj-y += cstate.o
>> endif
>>
>> i.e.,
>>
>> config ACPI_PROCESSOR
>> tristate "Processor"
>> depends on X86 || IA64 || ARM64
>> select ACPI_PROCESSOR_IDLE
>> select ACPI_CPU_FREQ_PSS if X86 || IA64
>>
>> Therefore, call_on_cpu() is only used when CONFIG_ACPI_CPU_FREQ_PSS=y.
>
> While technically kind of correct, this is also rather far from straightforward, because
> cstate.o and ACPI_CPU_FREQ_PSS are different things logically.
>
>> The #ifdef is rather a safe net that in the future, if we decided to make call_on_cpu()
>> a non-inline function, it will prevent triggering an compilation warning for unused
>> function when CONFIG_ACPI_CPU_FREQ_PSS=n.
>
> But as long as it is static inline, the #ifdef isn't necessary, is it?

Yes, the compiler yet to get an ability to warn about unused inline functions. I am not
going to insist for this tiny detail here. If nobody likes this #ifdef, I’ll happily remove it in v3.

>
>> It may also serve as a documentation purpose to indicate that function is only used
>> with CONFIG_ACPI_CPU_FREQ_PSS=y.
>
> Which is incidental and therefore misleading.
>
>>>
>>>> +static inline 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);
>>>> +}
>>>> +#endif
>>>> +
>>>> /* in processor_perflib.c */
>>>>
>>>> #ifdef CONFIG_CPU_FREQ

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