x86/dumpstack: Make stack name tags more comprehensible

NMI stack dumps are bracketed by the following tags:

  <NMI>
  ...
  <EOE>

The ending tag is kind of confusing if you don't already know what "EOE"
means (end of exception).  The same ending tag is also used to mark the
end of all other exceptions' stacks.  For example:

  <#DF>
  ...
  <EOE>

And similarly, "EOI" is used as the ending tag for interrupts:

  <IRQ>
  ...
  <EOI>

Change the tags to be more comprehensible by making them symmetrical and
more XML-esque:

  <NMI>
  ...
  </NMI>

  <#DF>
  ...
  </#DF>

  <IRQ>
  ...
  </IRQ>

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/180196e3754572540b595bc56b947d43658979a7.1479491159.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/stacktrace.h

@@ -30,8 +30,7 @@ bool in_task_stack(unsigned long *stack, struct task_struct *task,
 int get_stack_info(unsigned long *stack, struct task_struct *task,
 		   struct stack_info *info, unsigned long *visit_mask);
 
-void stack_type_str(enum stack_type type, const char **begin,
-		    const char **end);
+const char *stack_type_name(enum stack_type type);
 
 static inline bool on_stack(struct stack_info *info, void *addr, size_t len)
 {

arch/x86/kernel/dumpstack.c

@@ -76,7 +76,7 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	 * - hardirq stack
 	 */
 	for (regs = NULL; stack; stack = stack_info.next_sp) {
-		const char *str_begin, *str_end;
+		const char *stack_name;
 
 		/*
 		 * If we overflowed the task stack into a guard page, jump back
@@ -88,9 +88,9 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 		if (get_stack_info(stack, task, &stack_info, &visit_mask))
 			break;
 
-		stack_type_str(stack_info.type, &str_begin, &str_end);
-		if (str_begin)
-			printk("%s <%s>\n", log_lvl, str_begin);
+		stack_name = stack_type_name(stack_info.type);
+		if (stack_name)
+			printk("%s <%s>\n", log_lvl, stack_name);
 
 		/*
 		 * Scan the stack, printing any text addresses we find.  At the
@@ -155,8 +155,8 @@ void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 				__show_regs(regs, 0);
 		}
 
-		if (str_end)
-			printk("%s <%s>\n", log_lvl, str_end);
+		if (stack_name)
+			printk("%s </%s>\n", log_lvl, stack_name);
 	}
 }
 

arch/x86/kernel/dumpstack_32.c

@@ -16,18 +16,15 @@
 
 #include <asm/stacktrace.h>
 
-void stack_type_str(enum stack_type type, const char **begin, const char **end)
+const char *stack_type_name(enum stack_type type)
 {
-	switch (type) {
-	case STACK_TYPE_IRQ:
-	case STACK_TYPE_SOFTIRQ:
-		*begin = "IRQ";
-		*end   = "EOI";
-		break;
-	default:
-		*begin = NULL;
-		*end   = NULL;
-	}
+	if (type == STACK_TYPE_IRQ)
+		return "IRQ";
+
+	if (type == STACK_TYPE_SOFTIRQ)
+		return "SOFTIRQ";
+
+	return NULL;
 }
 
 static bool in_hardirq_stack(unsigned long *stack, struct stack_info *info)

arch/x86/kernel/dumpstack_64.c

@@ -28,23 +28,17 @@ static unsigned long exception_stack_sizes[N_EXCEPTION_STACKS] = {
 	[DEBUG_STACK - 1]			= DEBUG_STKSZ
 };
 
-void stack_type_str(enum stack_type type, const char **begin, const char **end)
+const char *stack_type_name(enum stack_type type)
 {
 	BUILD_BUG_ON(N_EXCEPTION_STACKS != 4);
 
-	switch (type) {
-	case STACK_TYPE_IRQ:
-		*begin = "IRQ";
-		*end   = "EOI";
-		break;
-	case STACK_TYPE_EXCEPTION ... STACK_TYPE_EXCEPTION_LAST:
-		*begin = exception_stack_names[type - STACK_TYPE_EXCEPTION];
-		*end   = "EOE";
-		break;
-	default:
-		*begin = NULL;
-		*end   = NULL;
-	}
+	if (type == STACK_TYPE_IRQ)
+		return "IRQ";
+
+	if (type >= STACK_TYPE_EXCEPTION && type <= STACK_TYPE_EXCEPTION_LAST)
+		return exception_stack_names[type - STACK_TYPE_EXCEPTION];
+
+	return NULL;
 }
 
 static bool in_exception_stack(unsigned long *stack, struct stack_info *info)