linux-kernel - Re: [PATCH] tracing: wake up tasks reading trace_pipe on write to trace

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Date:	Fri, 06 Aug 2010 17:29:35 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Marcin Slusarz <marcin.slusarz@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] tracing: wake up tasks reading trace_pipe on write to
 trace_marker

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


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