ftrace: comment arch ftrace code

Add comments to explain what is happening in the x86 arch ftrace code.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 428291581cb2441e3cab9e5fd9e28a150d6818e5..783455454d78dff61d14dcbaea05a2d07bcde605 100644 (file)
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -66,18 +66,23 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
        /*
         * Note: Due to modules and __init, code can
         *  disappear and change, we need to protect against faulting
-        *  as well as code changing.
+        *  as well as code changing. We do this by using the
+        *  __copy_*_user functions.
         *
         * No real locking needed, this code is run through
         * kstop_machine, or before SMP starts.
         */
+
+       /* read the text we want to modify */
        if (__copy_from_user_inatomic(replaced, (char __user *)ip,
                                      MCOUNT_INSN_SIZE))
                return -EFAULT;
 
+       /* Make sure it is what we expect it to be */
        if (memcmp(replaced, old_code, MCOUNT_INSN_SIZE) != 0)
                return -EINVAL;
 
+       /* replace the text with the new text */
        if (__copy_to_user_inatomic((char __user *)ip, new_code,
                                    MCOUNT_INSN_SIZE))
                return -EPERM;