Merge remote-tracking branches 'regmap/topic/rbtree' and 'regmap/topic/update-offload...

[karo-tx-linux.git] / arch / x86 / kernel / process.c

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 6d0e62ae8516760d6ae4af7deaa31418e82238fa..e28db181e4fcb04d19c02e7709e20fabb06f8c29 100644 (file)
--- 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_NOCHECK(*(unsigned long *)sp);
+       do {
+               if (fp < bottom || fp > top)
+                       return 0;
+               ip = READ_ONCE_NOCHECK(*(unsigned long *)(fp + sizeof(unsigned long)));
+               if (!in_sched_functions(ip))
+                       return ip;
+               fp = READ_ONCE_NOCHECK(*(unsigned long *)fp);
+       } while (count++ < 16 && p->state != TASK_RUNNING);
+       return 0;
+}