[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20081118134835.GC31146@elte.hu>
Date: Tue, 18 Nov 2008 14:48:35 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: ftrace: preemptoff selftest not working
* Heiko Carstens <heiko.carstens@...ibm.com> wrote:
> Hi Steven,
>
> I was wondering why the preemptoff and preemptirqsoff tracer
> selftests don't work on s390. After all its just that they get
> called from non-preemptible context:
>
> kernel_init() will execute all initcalls, however the first line in
> kernel_init() is lock_kernel(), which causes the preempt_count to be
> increased. Any later calls to add_preempt_count() (especially those
> from the selftests) will therefore not result in a call to
> trace_preempt_off() since the check below in add_preempt_count()
> will be false:
>
> if (preempt_count() == val)
> trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
>
> Hence the trace buffer will be empty.
ah, indeed :-)
side-effect of the removal of CONFIG_PREEMPT_BKL - these things were
written before that and nobody noticed that the self-test stopped
working for real.
> The patch below makes the selftests working for me, since then they
> run in preemptible context. But it is ugly and I'm not proposing it
> for upstream ;)
>
> Just wanted to make you aware that there is a bug.
indeed it's ugly. We could perhaps drop the BKL in the selftests?
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists