linux-kernel - Re: [PATCH 2/3] perf: Do not allow optimized switch for non-cloned events

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Date:	Tue, 24 Jun 2014 12:53:01 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [PATCH 2/3] perf: Do not allow optimized switch for non-cloned
 events

On Tue, Jun 24, 2014 at 12:39:36PM +0200, Peter Zijlstra wrote:
> On Tue, Jun 24, 2014 at 10:20:25AM +0200, Jiri Olsa wrote:
> > From: Jiri Olsa <jolsa@...hat.com>
> > 
> > The context check in perf_event_context_sched_out allows
> > non-cloned context to be part of the optimized schedule
> > out switch.
> > 
> > This could move non-cloned context into another workload
> > child. Once this child exits, the context is closed and
> > leaves all original (parent) events in closed state.
> > 
> > Any other new cloned event will have closed state and not
> > measure anything. And probably causing other odd bugs.
> > 
> > Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> > Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
> > Cc: David Ahern <dsahern@...il.com>
> > Cc: Frederic Weisbecker <fweisbec@...il.com>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Namhyung Kim <namhyung@...nel.org>
> > Cc: Paul Mackerras <paulus@...ba.org>
> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  kernel/events/core.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index d968008..4e3618e 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -2319,7 +2319,7 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
> >  	next_parent = rcu_dereference(next_ctx->parent_ctx);
> >  
> >  	/* If neither context have a parent context; they cannot be clones. */
> > -	if (!parent && !next_parent)
> > +	if (!parent || !next_parent)
> >  		goto unlock;
> >  
> >  	if (next_parent == ctx || next_ctx == parent || next_parent == parent) {
> 
> Ohh, nice, good catch!

should I queue it with your ack?

jirka
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