Date: Wed, 22 Oct 2014 06:39:57 +0000 (GMT)
From: Eunbong Song <eunb.song@samsung.com>
Subject: [PATCH] mips: add arch_trigger_all_cpu_backtrace() function
To: ralf@linux-mips.org
Cc: linux-mips@linux-mips.org, linux-kernel@vger.kernel.org
Reply-to: eunb.song@samsung.com
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Currently, arch_trigger_all_cpu_backtrace() is defined in only x86 and sparc which has nmi interrupt.
But in case of softlockup not a hardlockup, it could be possible to dump backtrace of all cpus. and this could be helpful for debugging.

for example, if system has 2 cpus.

	CPU 0				CPU 1
 acquire read_lock()

				try to do write_lock()

 ,,,
 missing read_unlock()

In this case, softlockup will occur becasuse CPU 0 does not call read_unlock().
And dump_stack() print only backtrace for "CPU 0". If CPU1's backtrace is printed it's very helpful.

This patch adds arch_trigger_all_cpu_backtrace() for mips architecture.

Maybe someone make better patch than this. I just suggest the idea.
---
 arch/mips/include/asm/irq.h |    3 +++
 arch/mips/kernel/process.c  |   18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/arch/mips/include/asm/irq.h b/arch/mips/include/asm/irq.h
index 39f07ae..5a4e1bb 100644
--- a/arch/mips/include/asm/irq.h
+++ b/arch/mips/include/asm/irq.h
@@ -48,4 +48,7 @@ extern int cp0_compare_irq;
 extern int cp0_compare_irq_shift;
 extern int cp0_perfcount_irq;
 
+void arch_trigger_all_cpu_backtrace(bool);
+#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
+
 #endif /* _ASM_IRQ_H */
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 636b074..9f51d3d 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -42,6 +42,7 @@
 #include <asm/isadep.h>
 #include <asm/inst.h>
 #include <asm/stacktrace.h>
+#include <asm/irq_regs.h>
 
 #ifdef CONFIG_HOTPLUG_CPU
 void arch_cpu_idle_dead(void)
@@ -532,3 +533,20 @@ unsigned long arch_align_stack(unsigned long sp)
 
 	return sp & ALMASK;
 }
+
+static void arch_dump_stack(void *info)
+{
+	struct pt_regs *regs;  
+	
+	regs = get_irq_regs();
+
+	if(regs)
+		show_regs(regs);
+
+	dump_stack();
+}
+
+void arch_trigger_all_cpu_backtrace(bool include_self)
+{
+	smp_call_function(arch_dump_stack, NULL, 1);
+}
-- 
1.7.0.1
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