MIPS: Add arch_trigger_all_cpu_backtrace() function

Currently, arch_trigger_all_cpu_backtrace() is defined in only x86 and
sparc which have an NMI.  But in case of softlockup, 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.

[ralf@linux-mips.org: Fixed whitespace and formatting issues.]
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8200/

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 */

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);
+}