[PATCH 1/3] ptrace_resume: set/clear PT_SINGLESTEP/PT_BLOCKSTEP

Contrary to the comment in ptrace.h, PT_SINGLESTEP is only used on
arch/xtensa, and PT_BLOCKSTEP is not used at all.

Change the arch independent ptrace_resume() to set/clear these bits
before user_enable_*_step/user_disable_single_step() and remove this
this code from arch/xtensa/kernel/ptrace.c.

Also change ptrace_init_task() to prevent the copying of these bits.

This doesn't make any difference on xtensa, and other arches do not
use these flags so far.

But, thereafter we can check task->ptrace & PT_*STEP to figure out if
this tracer wants the stepping and unlike TIF_SINGLESTEP it is always
correct in this sense and it is not arch dependent.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 include/linux/ptrace.h      |    4 ++--
 kernel/ptrace.c             |    3 +++
 arch/xtensa/kernel/ptrace.c |    2 --
 3 files changed, 5 insertions(+), 4 deletions(-)

--- ptrace/include/linux/ptrace.h~1_use_PT_STEP	2011-06-28 17:50:27.000000000 +0200
+++ ptrace/include/linux/ptrace.h	2011-07-03 21:55:17.000000000 +0200
@@ -104,7 +104,6 @@
 
 #define PT_TRACE_MASK	0x000003f4
 
-/* single stepping state bits (used on ARM and PA-RISC) */
 #define PT_SINGLESTEP_BIT	31
 #define PT_SINGLESTEP		(1<<PT_SINGLESTEP_BIT)
 #define PT_BLOCKSTEP_BIT	30
@@ -220,7 +219,8 @@ static inline void ptrace_init_task(stru
 	child->parent = child->real_parent;
 	child->ptrace = 0;
 	if (unlikely(ptrace) && (current->ptrace & PT_PTRACED)) {
-		child->ptrace = current->ptrace;
+		child->ptrace = current->ptrace &
+				~(PT_SINGLESTEP | PT_BLOCKSTEP);
 		__ptrace_link(child, current->parent);
 	}
 
--- ptrace/kernel/ptrace.c~1_use_PT_STEP	2011-06-28 17:50:27.000000000 +0200
+++ ptrace/kernel/ptrace.c	2011-07-03 21:55:17.000000000 +0200
@@ -599,13 +599,16 @@ static int ptrace_resume(struct task_str
 		clear_tsk_thread_flag(child, TIF_SYSCALL_EMU);
 #endif
 
+	child->ptrace &= ~(PT_SINGLESTEP | PT_BLOCKSTEP);
 	if (is_singleblock(request)) {
 		if (unlikely(!arch_has_block_step()))
 			return -EIO;
+		child->ptrace |= PT_BLOCKSTEP;
 		user_enable_block_step(child);
 	} else if (is_singlestep(request) || is_sysemu_singlestep(request)) {
 		if (unlikely(!arch_has_single_step()))
 			return -EIO;
+		child->ptrace |= PT_SINGLESTEP;
 		user_enable_single_step(child);
 	} else {
 		user_disable_single_step(child);
--- ptrace/arch/xtensa/kernel/ptrace.c~1_use_PT_STEP	2011-04-06 21:33:43.000000000 +0200
+++ ptrace/arch/xtensa/kernel/ptrace.c	2011-07-03 20:30:57.000000000 +0200
@@ -33,12 +33,10 @@
 
 void user_enable_single_step(struct task_struct *child)
 {
-	child->ptrace |= PT_SINGLESTEP;
 }
 
 void user_disable_single_step(struct task_struct *child)
 {
-	child->ptrace &= ~PT_SINGLESTEP;
 }
 
 /*