Subject: Re: [PATCH] tracing: wake up tasks reading trace_pipe on write to
 trace_marker
From: Steven Rostedt <rostedt@goodmis.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Marcin Slusarz <marcin.slusarz@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>
In-Reply-To: <20100806205549.GB5345@nowhere>
References: <20100727224408.GB4142@joi.lan>
	 <1281127136.3352.13.camel@gandalf.stny.rr.com>
	 <20100806205549.GB5345@nowhere>
Content-Type: text/plain; charset="ISO-8859-15"
Date: Fri, 06 Aug 2010 17:29:35 -0400
Message-ID: <1281130175.3352.15.camel@gandalf.stny.rr.com>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1298
Lines: 43

On Fri, 2010-08-06 at 22:55 +0200, Frederic Weisbecker wrote:

> > This can't work. trace_printk() and friends must be able to be used
> > anywhere. This can cause race conditions with the rq locks in the
> > scheduler.
> > 
> > But you do bring up a good idea. That is, perhaps we should have a way
> > to attach to known safe tracepoints that we can hook to to check if a
> > wake up should happen or not.
> 
> 
> This could be a simple macro that takes the name of the trace event:
> 
> 
> DEFINE_EVENT(event_tpl, event_name, ...);
> 
> 
> TRACE_EVENT_NO_WAKE(event_name);
> 

Yeah, that may be worth doing for 2.6.37. Might as well also add a
trace_printk_nowake() too, when you know you are in dangerous locations
like the scheduler or NMI.


> I think trace events should be wakeable by default as it looks safe for
> most of them. But probably we don't want that per event class.
> 
> In the unsafe list, I only have some sched and lock events in
> mind, but I bet there are some others.

Yep, will put that on my todo list.

Thanks,

-- Steve


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/