ftrace/sysprof: don't trace the user stack if we are a kernel thread.

Check that current->mm is non-NULL before attempting to trace the user
stack.

Also take depth of the kernel stack into account when comparing
against sample_max_depth.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 29 insertions, 21 deletions

diff --git a/kernel/trace/trace_sysprof.c b/kernel/trace/trace_sysprof.c
index fe23d6dba7f1..2301e1e7c606 100644
--- a/kernel/trace/trace_sysprof.c
+++ b/kernel/trace/trace_sysprof.c
@@ -95,13 +95,12 @@ const static struct stacktrace_ops backtrace_ops = {
         .address                = backtrace_address,
 };
 
-static struct pt_regs *
+static int
 trace_kernel(struct pt_regs *regs, struct trace_array *tr,
              struct trace_array_cpu *data)
 {
         struct backtrace_info info;
         unsigned long bp;
-        char *user_stack;
         char *stack;
 
         info.tr = tr;
@@ -119,10 +118,7 @@ trace_kernel(struct pt_regs *regs, struct trace_array *tr,
 
         dump_trace(NULL, regs, (void *)stack, bp, &backtrace_ops, &info);
 
-        /* Now trace the user stack */
-        user_stack = ((char *)current->thread.sp0 - sizeof(struct pt_regs));
-
-        return (struct pt_regs *)user_stack;
+        return info.pos;
 }
 
 static void timer_notify(struct pt_regs *regs, int cpu)
@@ -150,32 +146,44 @@ static void timer_notify(struct pt_regs *regs, int cpu)
         __trace_special(tr, data, 0, 0, current->pid);
 
         if (!is_user)
-                regs = trace_kernel(regs, tr, data);
+                i = trace_kernel(regs, tr, data);
+        else
+                i = 0;
 
-        fp = (void __user *)regs->bp;
+        /*
+         * Trace user stack if we are not a kernel thread
+         */
+        if (current->mm && i < sample_max_depth) {
+                regs = (struct pt_regs *)current->thread.sp0 - 1;
 
-        __trace_special(tr, data, 2, regs->ip, 0);
+                fp = (void __user *)regs->bp;
 
-        for (i = 0; i < sample_max_depth; i++) {
-                frame.next_fp = 0;
-                frame.return_address = 0;
-                if (!copy_stack_frame(fp, &frame))
-                        break;
-                if ((unsigned long)fp < regs->sp)
-                        break;
+                __trace_special(tr, data, 2, regs->ip, 0);
 
-                __trace_special(tr, data, 2, frame.return_address,
-                              (unsigned long)fp);
-                fp = frame.next_fp;
-        }
+                while (i < sample_max_depth) {
+                        frame.next_fp = 0;
+                        frame.return_address = 0;
+                        if (!copy_stack_frame(fp, &frame))
+                                break;
+                        if ((unsigned long)fp < regs->sp)
+                                break;
 
-        __trace_special(tr, data, 3, current->pid, i);
+                        __trace_special(tr, data, 2, frame.return_address,
+                                        (unsigned long)fp);
+                        fp = frame.next_fp;
+
+                        i++;
+                }
+
+        }
 
         /*
          * Special trace entry if we overflow the max depth:
          */
         if (i == sample_max_depth)
                 __trace_special(tr, data, -1, -1, -1);
+
+        __trace_special(tr, data, 3, current->pid, i);
 }
 
 static enum hrtimer_restart stack_trace_timer_fn(struct hrtimer *hrtimer)