Re: [PATCH] ACPI/OSL: Remove RCU in the osl.c to avoid dead lock with cpu hot plug

Lan Tianyu
2014-08-07T09:31:06Z

On 2014年08月07日 03:09, Rafael J. Wysocki wrote:
> On Wednesday, August 06, 2014 10:22:45 AM Lan Tianyu wrote:
>> On 2014年08月06日 09:24, Rafael J. Wysocki wrote:
>>> On Monday, August 04, 2014 04:40:08 PM Lan Tianyu wrote:
>
> [cut]
>
>>>> @@ -298,29 +298,29 @@ void __iomem *acpi_os_get_iomem(acpi_physical_address phys, unsigned int size)
>>>> {
>>>> struct acpi_ioremap *map;
>>>> void __iomem *virt = NULL;
>>>> + unsigned long flags;
>>>>
>>>> - mutex_lock(&acpi_ioremap_lock);
>>>> + spin_lock_irqsave(&acpi_ioremap_lock, flags);
>>>
>>> Why do you need to do _irqsave here? It was a mutex before, after all,
>>> so it can't be called from interrupt context.
>>>
>>> In other places below too.
>>
>> Original code uses RCU lock to protect acpi_ioremaps list in the
>> acpi_os_read/write_memory() which will be called in apei_read/write().
>> apei_read/write() will be called in the interrupt from APEI comments.
>
> But acpi_os_get_iomem() won't be called from interrupt context and should use
> spin_lock_irq() instead of _irqsave. This also applies to the other places
> that use the mutex.

Yes, that's correct. Sorry. I misunderstood what you meant.

>
>> Now replace RCU with acpi_ioremap_lock and the lock will be called in
>> the interrupt. So redefine it to spin lock. From history,
>> acpi_ioremap_lock was spin lock before adding RCU support.
>
> And it had scalability problems IIRC.
>
> Did you consider using SRCU instead of going back to the spinlock?

No, I will have a look at SRCU.

>
> Rafael
>

--
Best regards
Tianyu Lan