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

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Date:	Mon, 4 Jan 2010 20:30:44 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.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 01/04, Oleg Nesterov wrote:
>
> IOW. I think this problem is minor and probably can be ignored,

Or may be not...

Even if the child is not killed by SIGTRAP, it can get a lot of
unnecessary traps.

To verify, I did another trivial patch (below), and the test
case from 6580807da14c423f0d0a708108e6df6ebc8bc83d does trigger
a lot of "false step" printks.

Hmm. And sometimes there is nothing in dmesg, but the test-case
needs a lot of time to complete. "taskset -c" seems to always
trigger printk's. Magic.

Oleg.

--- arch/s390/kernel/traps.c~	2009-12-22 10:41:52.909174198 -0500
+++ arch/s390/kernel/traps.c	2010-01-04 13:19:51.038187586 -0500
@@ -384,6 +384,8 @@ void __kprobes do_single_step(struct pt_
 	}
 	if (tracehook_consider_fatal_signal(current, SIGTRAP))
 		force_sig(SIGTRAP, current);
+	else
+		printk("false step\n");
 }
 
 static void default_trap_handler(struct pt_regs * regs, long interruption_code)

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