Blackfin arch: Add basic irq stack checking for Blackfin

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

arch/blackfin/Kconfig.debug

@@ -2,6 +2,22 @@ menu "Kernel hacking"
 
 source "lib/Kconfig.debug"
 
+config DEBUG_STACKOVERFLOW
+	bool "Check for stack overflows"
+	depends on DEBUG_KERNEL
+	help
+	  This option will cause messages to be printed if free stack space
+	  drops below a certain limit.
+
+config DEBUG_STACK_USAGE
+	bool "Enable stack utilization instrumentation"
+	depends on DEBUG_KERNEL
+	help
+	  Enables the display of the minimum amount of free stack which each
+	  task has ever had available in the sysrq-T output.
+
+	  This option will slow down process creation somewhat.
+
 config HAVE_ARCH_KGDB
        def_bool y
 

arch/blackfin/include/asm/processor.h

@@ -24,6 +24,14 @@ static inline void wrusp(unsigned long usp)
 	__asm__ __volatile__("usp = %0;\n\t"::"da"(usp));
 }
 
+static inline unsigned long __get_SP(void)
+{
+	unsigned long sp;
+
+	__asm__ __volatile__("%0 = sp;\n\t" : "=da"(sp));
+	return sp;
+}
+
 /*
  * User space process size: 1st byte beyond user address space.
  * Fairly meaningless on nommu.  Parts of user programs can be scattered

arch/blackfin/include/asm/thread_info.h

@@ -44,6 +44,7 @@
  */
 #define THREAD_SIZE_ORDER	1
 #define THREAD_SIZE		8192	/* 2 pages */
+#define STACK_WARN		(THREAD_SIZE/8)
 
 #ifndef __ASSEMBLY__
 

arch/blackfin/kernel/irqchip.c

@@ -120,7 +120,21 @@ asmlinkage void asm_do_IRQ(unsigned int irq, struct pt_regs *regs)
 		desc = &bad_irq_desc;
 
 	irq_enter();
+#ifdef CONFIG_DEBUG_STACKOVERFLOW
+	/* Debugging check for stack overflow: is there less than STACK_WARN free? */
+	{
+		long sp;
 
+		sp = __get_SP() & (THREAD_SIZE-1);
+
+		if (unlikely(sp < (sizeof(struct thread_info) + STACK_WARN))) {
+			dump_stack();
+			printk(KERN_EMERG "%s: possible stack overflow while handling irq %i "
+					" only %ld bytes free\n",
+				__func__, irq, sp - sizeof(struct thread_info));
+		}
+	}
+#endif
 	generic_handle_irq(irq);
 
 	/* If we're the only interrupt running (ignoring IRQ15 which is for