linux-kernel - Re: [PATCH 3/3] Stop tracing on a schedule bug

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Date:	Fri, 16 Apr 2010 03:49:38 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Chase Douglas <chase.douglas@...onical.com>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...e.hu>,
	Randy Dunlap <randy.dunlap@...cle.com>
Subject: Re: [PATCH 3/3] Stop tracing on a schedule bug

On Fri, Apr 16, 2010 at 02:21:47AM +0200, Thomas Gleixner wrote:
> On Fri, 16 Apr 2010, Thomas Gleixner wrote:
> > BTW, if interacting with grub is that hard: how does an user start the
> > tracer at all ?
> 
> Just looked through the other patches and noticed that the patch which
> provides the tracing_off(level) stuff is incomplete as it provides
> only a command line option to change that tracing off level.
> 
> The command line option is merily for tracing which happens to be
> started on the command line i.e. _BEFORE_ we have usable user space.
> 
> So your grub argument is just crap. If the user cannot change this
> setting w/o fiddling with the obscured grub then he can not start the
> tracer on the command line either.
> 
> But somehow he can start the tracer later when user space is up and
> running, but there is no way to change that setting anymore. Therefor
> you go through the kernel and impose settings at will.
> 
> 1) Your patch simply lacks an interface to change that setting via
>    debugfs/tracing/wtf
> 
>    WTF should I reboot my machine to change that setting from the
>    default BUG to WARN or NONE ? There is no reason at all.
> 
> 2) tracing off can be done via filters on functions and/or events
>    already - so I doubt that the tracing_off_event(level) is necessary
>    at all.



Yeah it works for the function tracer, but not for events (or other tracers),
or I missed this feature somehow.

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