Re: [PATCH 1/2] fall back to old-style call trace if no unwinding is possible

["Jan Beulich" <jbeulich@novell.com>]

>hm, could you please merge this ontop of the stacktrace-output 
>beautification patch below that Andrew already has in his post-mm2 tree? 
>(or the other way around - whichever you prefer)

Here we go - but I'm afraid the patch you sent wasn't complete - even after resolving its rejects, it still had one
instance where the (now void) return value of printk_address() was used, and I would think all uses of the variable i in
show_trace() should go away then too (this variable was only used to track whether a second item should be printed on
the same line). Consequently, I'm afraid below patch still wouldn't apply to -mm...

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>

Index: 2.6.17-rc5-unwind-generic/arch/x86_64/kernel/traps.c
===================================================================
--- 2.6.17-rc5-unwind-generic.orig/arch/x86_64/kernel/traps.c	2006-06-02 14:24:43.000000000 +0200
+++ 2.6.17-rc5-unwind-generic/arch/x86_64/kernel/traps.c	2006-06-02 14:26:10.000000000 +0200
@@ -109,6 +109,7 @@ static inline void preempt_conditional_c
 }
 
 static int kstack_depth_to_print = 10;
+static int call_trace = 1;
 
 #ifdef CONFIG_KALLSYMS
 #include <linux/kallsyms.h> 
@@ -194,14 +195,18 @@ static unsigned long *in_exception_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 n = 0;
+
 	while (unwind(info) == 0 && UNW_PC(info)) {
+		++n;
 		printk_address(UNW_PC(info));
 		if (arch_unw_user_mode(info))
 			break;
 	}
 	printk("\n");
+	return n;
 }
 
 /*
@@ -215,27 +220,32 @@ void show_trace(struct task_struct *tsk,
 {
 	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;
-		}
-	} 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 (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);
+		}
+		if (unw_ret > 0) {
+			if (call_trace > 0)
+				return;
+			printk("Legacy call trace:");
+			i = 18;
 		}
 	}
 
@@ -261,7 +271,7 @@ void show_trace(struct task_struct *tsk,
 		} \
 	} while (0)
 
-	for(i = 11; ; ) {
+	for(; ; ) {
 		const char *id;
 		unsigned long *estack_end;
 		estack_end = in_exception_stack(cpu, (unsigned long)stack,
@@ -1049,3 +1059,14 @@ 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);
Index: 2.6.17-rc5-unwind-generic/include/asm-x86_64/unwind.h
===================================================================
--- 2.6.17-rc5-unwind-generic.orig/include/asm-x86_64/unwind.h	2006-06-02 14:24:43.000000000 +0200
+++ 2.6.17-rc5-unwind-generic/include/asm-x86_64/unwind.h	2006-06-02 14:26:10.000000000 +0200
@@ -75,10 +75,10 @@ static inline void arch_unw_init_blocked
 	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)
 {
Index: 2.6.17-rc5-unwind-generic/include/linux/unwind.h
===================================================================
--- 2.6.17-rc5-unwind-generic.orig/include/linux/unwind.h	2006-06-02 14:24:43.000000000 +0200
+++ 2.6.17-rc5-unwind-generic/include/linux/unwind.h	2006-06-02 14:29:27.000000000 +0200
@@ -49,8 +49,8 @@ extern int unwind_init_blocked(struct un
  * 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(st
 }
 
 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;
Index: 2.6.17-rc5-unwind-generic/kernel/unwind.c
===================================================================
--- 2.6.17-rc5-unwind-generic.orig/kernel/unwind.c	2006-06-02 14:24:43.000000000 +0200
+++ 2.6.17-rc5-unwind-generic/kernel/unwind.c	2006-06-02 14:29:27.000000000 +0200
@@ -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);