On Mon, 29 Aug 2016 00:07:27 +0530
Madhavan Srinivasan <ma...@linux.vnet.ibm.com> wrote:
> New Kconfig is added "CONFIG_IRQ_DEBUG_SUPPORT" to add a warn_on
> to alert the usage of soft_irq_set_mask() for disabling lower
> bitmask interrupts.
>
> Have also moved the code under the CONFIG_TRACE_IRQFLAGS in
> arch_local_irq_restore() to new Kconfig as suggested.
>
> Patch also adds a new soft_irq_set_mask() to update paca->soft_enabled.
>
> Signed-off-by: Madhavan Srinivasan <ma...@linux.vnet.ibm.com>
> ---
> arch/powerpc/Kconfig | 4 ++++
> arch/powerpc/include/asm/hw_irq.h | 17 +++++++++++++++++
> arch/powerpc/kernel/irq.c | 4 ++--
> 3 files changed, 23 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 927d2ab2ce08..878f05925340 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -51,6 +51,10 @@ config TRACE_IRQFLAGS_SUPPORT
> bool
> default y
>
> +config IRQ_DEBUG_SUPPORT
> + bool
> + default n
> +
> config LOCKDEP_SUPPORT
> bool
> default y
> diff --git a/arch/powerpc/include/asm/hw_irq.h
> b/arch/powerpc/include/asm/hw_irq.h
> index 415734c07cfa..9f71559ce868 100644
> --- a/arch/powerpc/include/asm/hw_irq.h
> +++ b/arch/powerpc/include/asm/hw_irq.h
> @@ -81,6 +81,23 @@ static inline unsigned long arch_local_irq_disable(void)
> return flags;
> }
>
> +static inline unsigned long soft_irq_set_mask(int value)
> +{
> + unsigned long flags, zero;
> +
> +#ifdef CONFIG_IRQ_DEBUG_SUPPORT
> + WARN_ON(value <= IRQ_DISABLE_MASK_LINUX);
> +#endif
> + asm volatile(
> + "li %1,%3; lbz %0,%2(13); stb %1,%2(13)"
> + : "=r" (flags), "=&r" (zero)
> + : "i" (offsetof(struct paca_struct, soft_enabled)),\
> + "i" (value)
> + : "memory");
> +
> + return flags;
> +}
One other thing, if we have:
local_irq_save(flags); // disable LINUX mask -> LINUX
local_irq_and_pmu_save(flags); // disable PMU mask -> LINUX|PMU
local_irq_and_pmu_restore(flags); // enable PMU mask -> LINUX
local_irq_restore(flags); // enable LINUX mask -> NONE
Then the nested code that re-enables PMUs will not replay PMU interrupt
until the outer irq is re-enabled. I don't *think* this is a problem,
but it probably should be commented.
Which brings us to arch_local_irq_restore() (from another patch):
@@ -208,7 +209,7 @@ notrace void arch_local_irq_restore(unsigned long en)
/* Write the new soft-enabled value */
set_soft_enabled(en);
- if (!en)
+ if (en == IRQ_DISABLE_MASK_LINUX)
return;
/*
* From this point onward, we can take interrupts, preempt,
I think this is a bit buggy for some cases of nested disables. For the
above it is okay, but if we have:
local_irq_and_pmu_save(flags);
local_irq_and_pmu_save(flags);
local_irq_and_pmu_restore(flags);
local_irq_and_pmu_restore(flags);
The first restore will restore LINUX|PMU mask, which will not be caught
by this check.
Testing instead for non-zero (any IRQ bits masked) should work. We should
probably also add an IRQ_DEBUG_SUPPORT check to ensure LINUX bit is always
one of the outer-most bits to be cleared (theoretically we could support
masking other bits without masking LINUX, but let's disallow that until a
compelling use case shows up).
Thanks,
Nick
