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

Martin Schwidefsky
2010-01-07T09:19:16Z

On Wed, 6 Jan 2010 13:13:29 -0800 (PST)
Roland McGrath <roland@redhat.com> wrote:

> > However, with or without CONFIG_UTRACE, 6580807da14c423f0d0a708108e6df6ebc8bc83d
> > is needed on s390 too, otherwise the child gets unnecessary traps.
>
> This confuses me. user_disable_single_step on non-current doesn't do
> anything not already done by the memset in copy_thread. Ooh, except
> perhaps it does not clear PSW_MASK_PER. Maybe that matters. That's
> the only thing I can think of. Maybe Martin can make sense of it.

The additional traps should not happen anymore with this patch:
--
Subject: [PATCH] clear TIF_SINGLE_STEP for new process.

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Clear the TIF_SINGLE_STEP bit in copy_thread. If the new process is
not auto-attached by the tracer it is wrong to delivere SIGTRAP to
the new process.

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

arch/s390/kernel/process.c | 1 +
1 file changed, 1 insertion(+)

diff -urpN linux-2.6/arch/s390/kernel/process.c linux-2.6-patched/arch/s390/kernel/process.c
--- linux-2.6/arch/s390/kernel/process.c 2009-12-03 04:51:21.000000000 +0100
+++ linux-2.6-patched/arch/s390/kernel/process.c 2010-01-07 09:25:53.000000000 +0100
@@ -217,6 +217,7 @@ int copy_thread(unsigned long clone_flag
p->thread.mm_segment = get_fs();
/* Don't copy debug registers */
memset(&p->thread.per_info, 0, sizeof(p->thread.per_info));
+ clear_tsk_thread_flag(p, TIF_SINGLE_STEP);
/* Initialize per thread user and system timer values */
ti = task_thread_info(p);
ti->user_timer = 0;
--
blue skies,
Martin.

"Reality continues to ruin my life." - Calvin.