Subject: Re: [BUG] next-20081216 - WARNING: at kernel/smp.c:333 smp_call_function_mask

From: Ingo Molnar <[email-masked]>
Date: Fri, 26 Dec 2008 19:17:34 +0100

* Kamalesh Babulal <[email-masked]> wrote:

> > how about the patch below, does that work too? (after removing 
> > Yinghai's patch)
> 
> Hi Ingo,
> 
> 	Kernel crashes with the same trace, after the applying the patch.

okay, thanks - does the below cleaner variant of Yinghai's patch solve the 
problem too?

	Ingo

-------------------->
>>From 9c93fc72ec95dc97d65b840978f9d605f4e5823a Mon Sep 17 00:00:00 2001
From: Yinghai Lu <[email-masked]>
Date: Fri, 26 Dec 2008 02:05:47 -0800
Subject: [PATCH] sparseirq: work around compiler optimizing away __weak functions

Impact: fix panic on null pointer with sparseirq

Some GCC versions seem to inline the weak global function,
when that function is empty.

Work it around, by putting a barrier into the function.

Signed-off-by: Yinghai <[email-masked]>
Signed-off-by: Ingo Molnar <[email-masked]>
---
 init/main.c         |    9 +++++++++
 kernel/irq/handle.c |    3 ++-
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/init/main.c b/init/main.c
index c1f999a..841d2b2 100644
--- a/init/main.c
+++ b/init/main.c
@@ -531,20 +531,29 @@ static void __init boot_cpu_init(void)
 	cpu_set(cpu, cpu_possible_map);
 }
 
+/*
+ * The barriers are needed to keep a GCC bug from optimizing
+ * away these weak functions:
+ */
+
 void __init __weak smp_setup_processor_id(void)
 {
+	barrier();
 }
 
 void __init __weak thread_info_cache_init(void)
 {
+	barrier();
 }
 
 void __init __weak arch_early_irq_init(void)
 {
+	barrier();
 }
 
 void __init __weak early_irq_init(void)
 {
+	barrier();
 	arch_early_irq_init();
 }
 
diff --git a/kernel/irq/handle.c b/kernel/irq/handle.c
index 06b05a4..a6d16a4 100644
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -86,8 +86,9 @@ void init_kstat_irqs(struct irq_desc *desc, int cpu, int nr)
 		desc->kstat_irqs = (unsigned int *)ptr;
 }
 
-void __attribute__((weak)) arch_init_chip_data(struct irq_desc *desc, int cpu)
+void __weak arch_init_chip_data(struct irq_desc *desc, int cpu)
 {
+	barrier();
 }
 
 static void init_one_irq_desc(int irq, struct irq_desc *desc, int cpu)