linux-kernel - Re: s390 && user_enable_single_step() (Was: odd utrace testing results on s390x)

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Date:	Thu, 7 Jan 2010 19:16:32 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Roland McGrath <roland@...hat.com>, caiqian@...hat.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Jan Kratochvil <jkratoch@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	utrace-devel@...hat.com
Subject: Re: s390 && user_enable_single_step() (Was: odd utrace testing
	results on s390x)

On 01/07, Martin Schwidefsky wrote:
>
> On Wed,  6 Jan 2010 13:08:12 -0800 (PST)
> Roland McGrath <roland@...hat.com> wrote:
>
> > That's what tracehook_signal_handler is for.  You're both doing it yourself
> > in the arch code (by setting TIF_SINGLE_STEP), and then telling the generic
> > code to do it (by passing stepping=1 to tracehook_signal_handler).
>
> Ok, so with the full utrace the semantics of tracehook_signal_handler
> is more than just causing a SIGTRAP. It is an indication for a signal
> AND a SIGTRAP if single-stepping is active. To make both cases work we
> should stop setting TIF_SINGLE_STEP in do_signal and pass
> current->thread.per_info.single_step to tracehook_signal_handler
> instead of test_thread_flag(TIF_SINGLE_STEP).

Can't understand why do we need TIF_SINGLE_STEP at all.

Just pass current->thread.per_info.single_step to
tracehook_signal_handler() ?

Oleg.

--- a/arch/s390/kernel/signal.c
+++ b/arch/s390/kernel/signal.c
@@ -504,14 +504,8 @@ void do_signal(struct pt_regs *regs)
 			 * for a normal instruction, act like we took
 			 * one for the handler setup.
 			 */
-			if (current->thread.per_info.single_step)
-				set_thread_flag(TIF_SINGLE_STEP);
-
-			/*
-			 * Let tracing know that we've done the handler setup.
-			 */
 			tracehook_signal_handler(signr, &info, &ka, regs,
-					 test_thread_flag(TIF_SINGLE_STEP));
+					 current->thread.per_info.single_step);
 		}
 		return;
 	}

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