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>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 428291581cb2..783455454d78 100644
--- 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;