s390/ptrace: clarify bits in the per_struct

The bits single_step and instruction_fetch lost their meaning
with git commit 5e9a26928f550157 "[S390] ptrace cleanup".
Clarify the comment for these two bits.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/include/uapi/asm/ptrace.h b/arch/s390/include/uapi/asm/ptrace.h
index a150f4fabe437a5f39ddcafb88c598895c909518..77630c74f13b13ea7510d0203aa35251c0f148a4 100644 (file)
--- a/arch/s390/include/uapi/asm/ptrace.h
+++ b/arch/s390/include/uapi/asm/ptrace.h
@@ -359,9 +359,9 @@ typedef struct
                per_cr_bits    bits;
        } control_regs;
        /*
-        * Use these flags instead of setting em_instruction_fetch
-        * directly they are used so that single stepping can be
-        * switched on & off while not affecting other tracing
+        * The single_step and instruction_fetch bits are obsolete,
+        * the kernel always sets them to zero. To enable single
+        * stepping use ptrace(PTRACE_SINGLESTEP) instead.
         */
        unsigned  single_step       : 1;
        unsigned  instruction_fetch : 1;