linux-kernel - Re: [PATCH 2/2] sched/debug: fix deadlock when enabling sched events

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Date:	Tue, 7 Jun 2016 16:02:37 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...hsingularity.net>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] sched/debug: fix deadlock when enabling sched events

On Tue, Jun 07, 2016 at 09:54:48PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 07, 2016 at 02:43:17PM -0500, Josh Poimboeuf wrote:
> > 1. Instead of just warning and allowing the tracepoints to be broken,
> >    I'd argue that it would be better to make them work by forcing
> >    schedstats enabled and printing a warning about that, which is what's
> 
> Forcing them enabled doesn't make them useful per se; some of these
> tracepoint rely on previously recoded state, which now wasn't previously
> recorded because back then it was disabled.

Ah, that's true.  Though this issue exists regardless of whether we
force enable schedstats or the user manually enables them.  It's a side
effect of allowing schedstats to be enabled after booting.

-- 
Josh