Re: [RFC PATCH v4 11/12] powerpc: Add a Kconfig and a function to set new soft_enabled mask

On Monday 05 September 2016 10:48 PM, Madhavan Srinivasan wrote:

On Monday 29 August 2016 07:11 AM, Nicholas Piggin wrote:

quoted

On Mon, 29 Aug 2016 00:07:27 +0530
Madhavan Srinivasan [off-list ref] wrote:

quoted

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 <redacted>
---
  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

Just sent out the newer version of the patchset with most of the comments addressed.
But I am not sure about this comment. IIUC, will something like this will do?

Sorry. Sent a wrong patch before along with the question..

#ifdef CONFIG_IRQ_DEBUG_SUPPORT
        WARN_ONCE (en & (en & IRQ_DISABLE_MASK_LINUX),
                   "soft_enabled transition to Unsupported state\n");
#endif