improve wchan reporting

diff -urN linus-2.5/arch/i386/kernel/process.c test/arch/i386/kernel/process.c
@@ -544,12 +544,15 @@
  */
 extern void scheduling_functions_start_here(void);
 extern void scheduling_functions_end_here(void);
-#define first_sched	((unsigned long) scheduling_functions_start_here)
-#define last_sched	((unsigned long) scheduling_functions_end_here)
+#define first_sched	((unsigned long) &scheduling_functions_start_here)
+#define last_sched	((unsigned long) &scheduling_functions_end_here)
+
+#define text_start	((unsigned long) &_stext)
+#define text_end	((unsigned long) &_etext)
 
 unsigned long get_wchan(struct task_struct *p)
 {
-	unsigned long ebp, esp, eip;
+	unsigned long ebp, esp, eip = 0;
 	unsigned long stack_page;
 	int count = 0;
 	if (!p || p == current || p->state == TASK_RUNNING)

@@ -560,13 +563,33 @@
 		return 0;
 	/* include/asm-i386/system.h:switch_to() pushes ebp last. */
 	ebp = *(unsigned long *) esp;
+
+	/* Our first attempt is to walk the chain of frame pointers. */
 	do {
-		if (ebp < stack_page || ebp > 8184+stack_page)
-			return 0;
+		if (ebp < stack_page || ebp > 8188+stack_page)
+			break;
 		eip = *(unsigned long *) (ebp+4);
+		if (eip < text_start || eip > text_end)
+			break;
 		if (eip < first_sched || eip >= last_sched)
 			return eip;
+
+		esp = ebp;
 		ebp = *(unsigned long *) ebp;
+		if (ebp <= esp || (ebp & 3))
+			break;
+	} while (count++ < 16);
+
+	/* Now try looking for a return address the hard way. */
+	do {
+		if (esp > 8188+stack_page)
+			break;
+		eip = *(unsigned long *)esp;
+
+		if (eip >= text_start && eip < text_end &&
+		    (eip < first_sched || eip >= last_sched))
+			return eip;
+		esp += 4;
 	} while (count++ < 16);
 	return 0;
 }

diff -urN linus-2.5/arch/i386/kernel/semaphore.c test/arch/i386/kernel/semaphore.c
@@ -53,6 +53,7 @@
 	wake_up(&sem->wait);
 }
 
+void __down(struct semaphore * sem) ATTRIB_NOWCHAN;
 void __down(struct semaphore * sem)
 {
 	struct task_struct *tsk = current;

@@ -90,6 +91,7 @@
 	tsk->state = TASK_RUNNING;
 }
 
+int __down_interruptible(struct semaphore * sem) ATTRIB_NOWCHAN;
 int __down_interruptible(struct semaphore * sem)
 {
 	int retval = 0;

@@ -187,10 +189,12 @@
  * value..
  */
 asm(
-".text\n"
+".section .text.scheduler, \"ax\"\n"
 ".align 4\n"
 ".globl __down_failed\n"
 "__down_failed:\n\t"
+	"pushl %ebp\n\t"
+	"movl %esp,%ebp\n\t"
 	"pushl %eax\n\t"
 	"pushl %edx\n\t"
 	"pushl %ecx\n\t"

@@ -198,20 +202,26 @@
 	"popl %ecx\n\t"
 	"popl %edx\n\t"
 	"popl %eax\n\t"
-	"ret"
+	"popl %ebp\n\t"
+	"ret\n"
+".previous"
 );
 
 asm(
-".text\n"
+".section .text.scheduler, \"ax\"\n"
 ".align 4\n"
 ".globl __down_failed_interruptible\n"
 "__down_failed_interruptible:\n\t"
+	"pushl %ebp\n\t"
+	"movl %esp,%ebp\n\t"
 	"pushl %edx\n\t"
 	"pushl %ecx\n\t"
 	"call __down_interruptible\n\t"
 	"popl %ecx\n\t"
 	"popl %edx\n\t"
-	"ret"
+	"popl %ebp\n\t"
+	"ret\n"
+".previous"
 );
 
 asm(

diff -urN linus-2.5/include/linux/linkage.h test/include/linux/linkage.h
@@ -35,6 +35,9 @@
 #define ATTRIB_NORET  __attribute__((noreturn))
 #define NORET_AND     noreturn,
 
+/* For use by functions that we do not want showing up in the wchan listing */
+#define ATTRIB_NOWCHAN        __attribute__((section(".text.scheduler")))
+
 #ifndef FASTCALL
 #define FASTCALL(x)	x
 #endif

diff -urN linus-2.5/kernel/sched.c test/kernel/sched.c
@@ -931,11 +931,10 @@
 	spin_unlock(&rq->lock);
 }
 
-void scheduling_functions_start_here(void) { }
-
 /*
  * schedule() is the main scheduler function.
  */
+asmlinkage void schedule(void) ATTRIB_NOWCHAN;
 asmlinkage void schedule(void)
 {
 	task_t *prev, *next;

@@ -1041,6 +1040,7 @@
  * off of preempt_enable.  Kernel preemptions off return from interrupt
  * occur there and call schedule directly.
  */
+asmlinkage void preempt_schedule(void) ATTRIB_NOWCHAN;
 asmlinkage void preempt_schedule(void)
 {
 	struct thread_info *ti = current_thread_info();

@@ -1161,6 +1161,7 @@
 	spin_unlock_irqrestore(&x->wait.lock, flags);
 }
 
+void wait_for_completion(struct completion *x) ATTRIB_NOWCHAN;
 void wait_for_completion(struct completion *x)
 {
 	might_sleep();

@@ -1197,6 +1198,7 @@
 	__remove_wait_queue(q, &wait);				\
 	spin_unlock_irqrestore(&q->lock, flags);
 
+void interruptible_sleep_on(wait_queue_head_t *q) ATTRIB_NOWCHAN;
 void interruptible_sleep_on(wait_queue_head_t *q)
 {
 	SLEEP_ON_VAR

@@ -1208,6 +1210,7 @@
 	SLEEP_ON_TAIL
 }
 
+long interruptible_sleep_on_timeout(wait_queue_head_t *q, long timeout) ATTRIB_NOWCHAN;
 long interruptible_sleep_on_timeout(wait_queue_head_t *q, long timeout)
 {
 	SLEEP_ON_VAR

@@ -1221,6 +1224,7 @@
 	return timeout;
 }
 
+void sleep_on(wait_queue_head_t *q) ATTRIB_NOWCHAN;
 void sleep_on(wait_queue_head_t *q)
 {
 	SLEEP_ON_VAR

@@ -1232,6 +1236,7 @@
 	SLEEP_ON_TAIL
 }
 
+long sleep_on_timeout(wait_queue_head_t *q, long timeout) ATTRIB_NOWCHAN;
 long sleep_on_timeout(wait_queue_head_t *q, long timeout)
 {
 	SLEEP_ON_VAR

@@ -1245,8 +1250,6 @@
 	return timeout;
 }
 
-void scheduling_functions_end_here(void) { }
-
 void set_user_nice(task_t *p, long nice)
 {
 	unsigned long flags;

diff -urN linus-2.5/kernel/timer.c test/kernel/timer.c
@@ -853,6 +853,7 @@
  *
  * In all cases the return value is guaranteed to be non-negative.
  */
+signed long schedule_timeout(signed long timeout) ATTRIB_NOWCHAN;
 signed long schedule_timeout(signed long timeout)
 {
 	timer_t timer;