Q: what user_enable_single_step() actually means?

[Oleg Nesterov]

On 09/21, Oleg Nesterov wrote:
>
> Looks like, ptrace can't rely on user_enable_single_step(), unless the syscall
> was entered with _TIF_SYSCALL_TRACE/_TIF_SINGLESTEP or we are going to return
> with signal.

And there is another issue: finish_resume_report(UTRACE_RESUME) does
user_disable_single_step().

Now I _hope_ I fully understand why my initial patch to handle PTRACE_SINGLESTEP
didn't work. report_signal/quiesce should re-assert SINGLESTEP, it should be
recorded in ptrace_context.

With the test patch below on top of "[PATCH 50] ptrace_request: use ptrace_lookup_engine()"
the kernel passes these tests

	step-jump-cont
	step-to-breakpoint
	step-simple

These
	step-into-handler
	step-through-sigret

fail, but I think this is understandable: ptrace_report_signal() doen't
process UTRACE_SIGNAL_HANDLER yet.



Now I need to think a bit more before I send the PTRACE_SINGLESTEP changes.
And perhaps you can shed more light on enable_disable_single_step() magic...

Oleg.


--- PU/kernel/utrace.c~TF_FBG	2009-09-15 10:34:59.000000000 +0200
+++ PU/kernel/utrace.c	2009-09-21 22:42:15.000000000 +0200
@@ -1765,7 +1765,7 @@ static void finish_resume_report(struct 
 	case UTRACE_REPORT:
 	case UTRACE_RESUME:
 	default:
-		user_disable_single_step(task);
+		//user_disable_single_step(task);
 		break;
 	}
 }
--- PU/kernel/ptrace.c~51_STEP_SIMPLE	2009-09-17 21:03:11.000000000 +0200
+++ PU/kernel/ptrace.c	2009-09-21 19:52:55.000000000 +0200
@@ -924,6 +924,7 @@ static void ptrace_wake_up(struct utrace
 
 static void do_ptrace_resume(struct utrace_engine *engine,
 				struct task_struct *tracee,
+				enum utrace_resume_action action,
 				long request, long data)
 {
 	struct ptrace_context *context = ptrace_context(engine);
@@ -950,7 +951,7 @@ static void do_ptrace_resume(struct utra
 		}
 	}
 
-	ptrace_wake_up(engine, tracee, UTRACE_RESUME);
+	ptrace_wake_up(engine, tracee, action);
 }
 
 static int ptrace_resume(struct utrace_engine *engine,
@@ -992,7 +993,7 @@ static int ptrace_resume(struct utrace_e
 	}
 
 	if (!ret)
-		do_ptrace_resume(engine, child, request, data);
+		do_ptrace_resume(engine, child, action, request, data);
 
 	return ret;
 }