linux-kernel - [ 009/187] powerpc: check_and_cede

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Date:	Thu, 12 Jul 2012 15:32:45 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Anton Blanchard <anton@...ba.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: [ 009/187] powerpc: check_and_cede_processor() never cedes

From: Greg KH <gregkh@...uxfoundation.org>

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Anton Blanchard <anton@...ba.org>

commit 0b17ba7258db83cd02da560884e053b85de371f2 upstream.

Commit f948501b36c6 ("Make hard_irq_disable() actually hard-disable
interrupts") caused check_and_cede_processor to stop working.
->irq_happened will never be zero right after a hard_irq_disable
so the compiler removes the call to cede_processor completely.

The bug was introduced back in the lazy interrupt handling rework
of 3.4 but was hidden until recently because hard_irq_disable did
nothing.

This issue will eventually appear in 3.4 stable since the
hard_irq_disable fix is marked stable, so mark this one for stable
too.

Signed-off-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/include/asm/hw_irq.h               |    5 +++++
 arch/powerpc/platforms/pseries/processor_idle.c |    2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

--- a/arch/powerpc/include/asm/hw_irq.h
+++ b/arch/powerpc/include/asm/hw_irq.h
@@ -102,6 +102,11 @@ static inline void hard_irq_disable(void
 /* include/linux/interrupt.h needs hard_irq_disable to be a macro */
 #define hard_irq_disable	hard_irq_disable
 
+static inline bool lazy_irq_pending(void)
+{
+	return !!(get_paca()->irq_happened & ~PACA_IRQ_HARD_DIS);
+}
+
 /*
  * This is called by asynchronous interrupts to conditionally
  * re-enable hard interrupts when soft-disabled after having
--- a/arch/powerpc/platforms/pseries/processor_idle.c
+++ b/arch/powerpc/platforms/pseries/processor_idle.c
@@ -106,7 +106,7 @@ static void check_and_cede_processor(voi
 	 * we first hard disable then check.
 	 */
 	hard_irq_disable();
-	if (get_paca()->irq_happened == 0)
+	if (!lazy_irq_pending())
 		cede_processor();
 }
 


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