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

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Message-ID: <20100104171626.22ea2d9c@mschwide.boeblingen.de.ibm.com>
Date:	Mon, 4 Jan 2010 17:16:26 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	caiqian@...hat.com, Heiko Carstens <heiko.carstens@...ibm.com>,
	Jan Kratochvil <jkratoch@...hat.com>,
	Roland McGrath <roland@...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 Mon, 4 Jan 2010 16:52:25 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> Hi!
> 
> We have some strange problems with utrace on s390, and so far this _looks_
> like a s390 problem.
> 
> Looks like, on any CPU user_enable_single_step() does not "work" until at
> least one thread with per_info.single_step = 1 does the context switch.
> 
> This doesn't matter with the old ptrace implementation, but with utrace
> the tracee itself does user_enable_single_step(current) and returns to
> user-mode. Until it does at least one context switch the single-stepping
> doesn't work, after that everything works fine till the next reboot.

The PER control registers only get reloaded on task switch. Can you test
if this patch fixes your problem?

--
Subject: [PATCH] fix loading of PER control registers for utrace.

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

If the current task enables / disables PER tracing for itself the
PER control registers need to be loaded in FixPerRegisters.

Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
---
 arch/s390/kernel/ptrace.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/arch/s390/kernel/ptrace.c
+++ b/arch/s390/kernel/ptrace.c
@@ -98,6 +98,9 @@ FixPerRegisters(struct task_struct *task
 		per_info->control_regs.bits.storage_alt_space_ctl = 1;
 	else
 		per_info->control_regs.bits.storage_alt_space_ctl = 0;
+
+	if (task == current)
+		__ctl_load(per_info->control_regs.words, 9, 11);
 }
 
 void user_enable_single_step(struct task_struct *task)

-- 
blue skies,
   Martin.

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

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