[PATCH] i386/x86-64: fall back to old-style call trace if no unwinding

If no unwinding is possible at all for a certain exception instance,
fall back to the old style call trace instead of not showing any trace
at all.

Also, allow setting the stack trace mode at the command line.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/traps.c

@@ -93,6 +93,7 @@ asmlinkage void spurious_interrupt_bug(void);
 asmlinkage void machine_check(void);
 
 static int kstack_depth_to_print = 24;
+static int call_trace = 1;
 ATOMIC_NOTIFIER_HEAD(i386die_chain);
 
 int register_die_notifier(struct notifier_block *nb)
@@ -171,40 +172,47 @@ static inline unsigned long print_context_stack(struct thread_info *tinfo,
 	return ebp;
 }
 
-static asmlinkage void show_trace_unwind(struct unwind_frame_info *info, void *log_lvl)
+static asmlinkage int show_trace_unwind(struct unwind_frame_info *info, void *log_lvl)
 {
+	int n = 0;
 	int printed = 0; /* nr of entries already printed on current line */
 
 	while (unwind(info) == 0 && UNW_PC(info)) {
+		++n;
 		printed = print_addr_and_symbol(UNW_PC(info), log_lvl, printed);
 		if (arch_unw_user_mode(info))
 			break;
 	}
 	if (printed)
 		printk("\n");
+	return n;
 }
 
 static void show_trace_log_lvl(struct task_struct *task, struct pt_regs *regs,
 			       unsigned long *stack, char *log_lvl)
 {
 	unsigned long ebp;
-	struct unwind_frame_info info;
 
 	if (!task)
 		task = current;
 
-	if (regs) {
-		if (unwind_init_frame_info(&info, task, regs) == 0) {
-			show_trace_unwind(&info, log_lvl);
-			return;
+	if (call_trace >= 0) {
+		int unw_ret = 0;
+		struct unwind_frame_info info;
+
+		if (regs) {
+			if (unwind_init_frame_info(&info, task, regs) == 0)
+				unw_ret = show_trace_unwind(&info, log_lvl);
+		} else if (task == current)
+			unw_ret = unwind_init_running(&info, show_trace_unwind, log_lvl);
+		else {
+			if (unwind_init_blocked(&info, task) == 0)
+				unw_ret = show_trace_unwind(&info, log_lvl);
 		}
-	} else if (task == current) {
-		if (unwind_init_running(&info, show_trace_unwind, log_lvl) == 0)
-			return;
-	} else {
-		if (unwind_init_blocked(&info, task) == 0) {
-			show_trace_unwind(&info, log_lvl);
-			return;
+		if (unw_ret > 0) {
+			if (call_trace > 0)
+				return;
+			printk("%sLegacy call trace:\n", log_lvl);
 		}
 	}
 
@@ -1245,3 +1253,15 @@ static int __init kstack_setup(char *s)
 	return 1;
 }
 __setup("kstack=", kstack_setup);
+
+static int __init call_trace_setup(char *s)
+{
+	if (strcmp(s, "old") == 0)
+		call_trace = -1;
+	else if (strcmp(s, "both") == 0)
+		call_trace = 0;
+	else if (strcmp(s, "new") == 0)
+		call_trace = 1;
+	return 1;
+}
+__setup("call_trace=", call_trace_setup);

arch/x86_64/kernel/traps.c

@@ -107,6 +107,7 @@ static inline void preempt_conditional_cli(struct pt_regs *regs)
 }
 
 static int kstack_depth_to_print = 10;
+static int call_trace = 1;
 
 #ifdef CONFIG_KALLSYMS
 #include <linux/kallsyms.h> 
@@ -190,11 +191,12 @@ static unsigned long *in_exception_stack(unsigned cpu, unsigned long stack,
 	return NULL;
 }
 
-static void show_trace_unwind(struct unwind_frame_info *info, void *context)
+static int show_trace_unwind(struct unwind_frame_info *info, void *context)
 {
-	int i = 11;
+	int i = 11, n = 0;
 
 	while (unwind(info) == 0 && UNW_PC(info)) {
+		++n;
 		if (i > 50) {
 			printk("\n       ");
 			i = 7;
@@ -205,6 +207,7 @@ static void show_trace_unwind(struct unwind_frame_info *info, void *context)
 			break;
 	}
 	printk("\n");
+	return n;
 }
 
 /*
@@ -218,27 +221,32 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
 {
 	const unsigned cpu = safe_smp_processor_id();
 	unsigned long *irqstack_end = (unsigned long *)cpu_pda(cpu)->irqstackptr;
-	int i;
+	int i = 11;
 	unsigned used = 0;
-	struct unwind_frame_info info;
 
 	printk("\nCall Trace:");
 
 	if (!tsk)
 		tsk = current;
 
-	if (regs) {
-		if (unwind_init_frame_info(&info, tsk, regs) == 0) {
-			show_trace_unwind(&info, NULL);
-			return;
+	if (call_trace >= 0) {
+		int unw_ret = 0;
+		struct unwind_frame_info info;
+
+		if (regs) {
+			if (unwind_init_frame_info(&info, tsk, regs) == 0)
+				unw_ret = show_trace_unwind(&info, NULL);
+		} else if (tsk == current)
+			unw_ret = unwind_init_running(&info, show_trace_unwind, NULL);
+		else {
+			if (unwind_init_blocked(&info, tsk) == 0)
+				unw_ret = show_trace_unwind(&info, NULL);
 		}
-	} else if (tsk == current) {
-		if (unwind_init_running(&info, show_trace_unwind, NULL) == 0)
-			return;
-	} else {
-		if (unwind_init_blocked(&info, tsk) == 0) {
-			show_trace_unwind(&info, NULL);
-			return;
+		if (unw_ret > 0) {
+			if (call_trace > 0)
+				return;
+			printk("Legacy call trace:");
+			i = 18;
 		}
 	}
 
@@ -264,7 +272,7 @@ void show_trace(struct task_struct *tsk, struct pt_regs *regs, unsigned long * s
 		} \
 	} while (0)
 
-	for(i = 11; ; ) {
+	for(; ; ) {
 		const char *id;
 		unsigned long *estack_end;
 		estack_end = in_exception_stack(cpu, (unsigned long)stack,
@@ -1052,3 +1060,14 @@ static int __init kstack_setup(char *s)
 }
 __setup("kstack=", kstack_setup);
 
+static int __init call_trace_setup(char *s)
+{
+	if (strcmp(s, "old") == 0)
+		call_trace = -1;
+	else if (strcmp(s, "both") == 0)
+		call_trace = 0;
+	else if (strcmp(s, "new") == 0)
+		call_trace = 1;
+	return 1;
+}
+__setup("call_trace=", call_trace_setup);

include/asm-i386/unwind.h

@@ -66,10 +66,10 @@ static inline void arch_unw_init_blocked(struct unwind_frame_info *info)
 	info->regs.xes = __USER_DS;
 }
 
-extern asmlinkage void arch_unwind_init_running(struct unwind_frame_info *,
-                                                asmlinkage void (*callback)(struct unwind_frame_info *,
-                                                                            void *arg),
-                                                void *arg);
+extern asmlinkage int arch_unwind_init_running(struct unwind_frame_info *,
+                                               asmlinkage int (*callback)(struct unwind_frame_info *,
+                                                                          void *arg),
+                                               void *arg);
 
 static inline int arch_unw_user_mode(const struct unwind_frame_info *info)
 {

include/asm-x86_64/unwind.h

@@ -75,10 +75,10 @@ static inline void arch_unw_init_blocked(struct unwind_frame_info *info)
 	info->regs.ss = __KERNEL_DS;
 }
 
-extern void arch_unwind_init_running(struct unwind_frame_info *,
-                                     void (*callback)(struct unwind_frame_info *,
-                                                      void *arg),
-                                     void *arg);
+extern int arch_unwind_init_running(struct unwind_frame_info *,
+                                    int (*callback)(struct unwind_frame_info *,
+                                                    void *arg),
+                                    void *arg);
 
 static inline int arch_unw_user_mode(const struct unwind_frame_info *info)
 {

include/linux/unwind.h

@@ -49,8 +49,8 @@ extern int unwind_init_blocked(struct unwind_frame_info *,
  * Prepare to unwind the currently running thread.
  */
 extern int unwind_init_running(struct unwind_frame_info *,
-                               asmlinkage void (*callback)(struct unwind_frame_info *,
-                                                           void *arg),
+                               asmlinkage int (*callback)(struct unwind_frame_info *,
+                                                          void *arg),
                                void *arg);
 
 /*
@@ -97,8 +97,8 @@ static inline int unwind_init_blocked(struct unwind_frame_info *info,
 }
 
 static inline int unwind_init_running(struct unwind_frame_info *info,
-                                      asmlinkage void (*cb)(struct unwind_frame_info *,
-                                                            void *arg),
+                                      asmlinkage int (*cb)(struct unwind_frame_info *,
+                                                           void *arg),
                                       void *arg)
 {
 	return -ENOSYS;

kernel/unwind.c

@@ -885,14 +885,13 @@ EXPORT_SYMBOL(unwind_init_blocked);
  * Prepare to unwind the currently running thread.
  */
 int unwind_init_running(struct unwind_frame_info *info,
-                        asmlinkage void (*callback)(struct unwind_frame_info *,
-                                                    void *arg),
+                        asmlinkage int (*callback)(struct unwind_frame_info *,
+                                                   void *arg),
                         void *arg)
 {
 	info->task = current;
-	arch_unwind_init_running(info, callback, arg);
 
-	return 0;
+	return arch_unwind_init_running(info, callback, arg);
 }
 EXPORT_SYMBOL(unwind_init_running);