linux-kernel - Re: [PATCH 2/3] trace: fix default boot up tracer

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Message-ID: <20090203052913.GC28361@elte.hu>
Date:	Tue, 3 Feb 2009 06:29:13 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/3] trace: fix default boot up tracer


* Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt <srostedt@...hat.com>
> 
> Peter Zijlstra started the functionality to start up a default
> tracing at bootup. This patch finishes the work.
> 
> Now if you add 'ftrace=<tracer>' to the command line, when that tracer
> is registered on bootup, that tracer is selected and starts tracing.
> 
> Note, all selftests for tracers that are registered after this tracer
> is disabled. This prevents the selftests from disturbing the running
> tracer, or the running tracer from disturbing the selftest.
> 
> Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> ---
>  kernel/trace/trace.c |   60 +++++++++++++++++++++++++++++++++++++++++++++-----
>  1 files changed, 54 insertions(+), 6 deletions(-)

applied to tip/tracing/ftrace, thanks Steve!

This portion is a bit ugly:

> -	lock_kernel();
>  
> +	if (!ret && default_bootup_tracer) {
> +		if (!strncmp(default_bootup_tracer, type->name,
> +			     BOOTUP_TRACER_SIZE)) {
> +			printk(KERN_INFO "Starting tracer '%s'\n",
> +			       type->name);
> +			/* Do we want this tracer to start on bootup? */
> +			tracing_set_tracer(type->name);
> +			default_bootup_tracer = NULL;
> +			/* disable other selftests, since this will break it. */
> +			tracing_selftest_disabled = 1;
> +#ifdef CONFIG_FTRACE_STARTUP_TEST
> +			printk(KERN_INFO "Disabling FTRACE selftests due"
> +			       " to running tracer '%s'\n", type->name);
> +#endif
> +		}
> +	}
> +
> +	lock_kernel();
>  	return ret;

This could be done as:

	if (ret || default_bootup_tracer)
		goto out_relock;

	if (strncmp(default_bootup_tracer, type->name, BOOTUP_TRACER_SIZE)) 
		goto out_relock;

	...

 out_relock:
	lock_kernel();
	return ret;

And we lose a lot of crappy linebreaks that way as well - beyond making the 
purpose of the BKL bits clearer. Hm?

	Ingo

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