uml: implement get_wchan

Implement get_wchan - the algorithm is similar to x86.  It starts with the
stack pointer of the process in question and looks above that for addresses
that are kernel text.  The second one which isn't in the scheduler is the one
that's returned.  The first one is ignored because that will be UML's own
context switching routine.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/arch/um/kernel/process.c b/arch/um/kernel/process.c
index 0eae00b..c7ea7f2 100644
--- a/arch/um/kernel/process.c
+++ b/arch/um/kernel/process.c
@@ -459,3 +459,38 @@ unsigned long arch_align_stack(unsigned long sp)
 	return sp & ~0xf;
 }
 #endif
+
+unsigned long get_wchan(struct task_struct *p)
+{
+	unsigned long stack_page, sp, ip;
+	bool seen_sched = 0;
+
+	if ((p == NULL) || (p == current) || (p->state == TASK_RUNNING))
+		return 0;
+
+	stack_page = (unsigned long) task_stack_page(p);
+	/* Bail if the process has no kernel stack for some reason */
+	if (stack_page == 0)
+		return 0;
+
+	sp = p->thread.switch_buf->JB_SP;
+	/*
+	 * Bail if the stack pointer is below the bottom of the kernel
+	 * stack for some reason
+	 */
+	if (sp < stack_page)
+		return 0;
+
+	while (sp < stack_page + THREAD_SIZE) {
+		ip = *((unsigned long *) sp);
+		if (in_sched_functions(ip))
+			/* Ignore everything until we're above the scheduler */
+			seen_sched = 1;
+		else if (kernel_text_address(ip) && seen_sched)
+			return ip;
+
+		sp += sizeof(unsigned long);
+	}
+
+	return 0;
+}