1 files changed, 55 insertions, 0 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 6d0e62ae8516..39e585a554b7 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -506,3 +506,58 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
         return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
 }
 
+/*
+ * Called from fs/proc with a reference on @p to find the function
+ * which called into schedule(). This needs to be done carefully
+ * because the task might wake up and we might look at a stack
+ * changing under us.
+ */
+unsigned long get_wchan(struct task_struct *p)
+{
+        unsigned long start, bottom, top, sp, fp, ip;
+        int count = 0;
+
+        if (!p || p == current || p->state == TASK_RUNNING)
+                return 0;
+
+        start = (unsigned long)task_stack_page(p);
+        if (!start)
+                return 0;
+
+        /*
+         * Layout of the stack page:
+         *
+         * ----------- topmax = start + THREAD_SIZE - sizeof(unsigned long)
+         * PADDING
+         * ----------- top = topmax - TOP_OF_KERNEL_STACK_PADDING
+         * stack
+         * ----------- bottom = start + sizeof(thread_info)
+         * thread_info
+         * ----------- start
+         *
+         * The tasks stack pointer points at the location where the
+         * framepointer is stored. The data on the stack is:
+         * ... IP FP ... IP FP
+         *
+         * We need to read FP and IP, so we need to adjust the upper
+         * bound by another unsigned long.
+         */
+        top = start + THREAD_SIZE - TOP_OF_KERNEL_STACK_PADDING;
+        top -= 2 * sizeof(unsigned long);
+        bottom = start + sizeof(struct thread_info);
+
+        sp = READ_ONCE(p->thread.sp);
+        if (sp < bottom || sp > top)
+                return 0;
+
+        fp = READ_ONCE(*(unsigned long *)sp);
+        do {
+                if (fp < bottom || fp > top)
+                        return 0;
+                ip = READ_ONCE(*(unsigned long *)(fp + sizeof(unsigned long)));
+                if (!in_sched_functions(ip))
+                        return ip;
+                fp = READ_ONCE(*(unsigned long *)fp);
+        } while (count++ < 16 && p->state != TASK_RUNNING);
+        return 0;
+}