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

Rafael J. Wysocki
2014-08-06T18:50:45Z

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.

> 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?

Rafael

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