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