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Message-ID: <20151211170029.GI6373@twins.programming.kicks-ass.net>
Date: Fri, 11 Dec 2015 18:00:29 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
vince@...ter.net, eranian@...gle.com,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCH v0 3/5] perf: Introduce instruction trace filtering
On Fri, Dec 11, 2015 at 04:28:54PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 11, 2015 at 03:36:36PM +0200, Alexander Shishkin wrote:
>
> > @@ -9063,6 +9621,18 @@ inherit_event(struct perf_event *parent_event,
> > get_ctx(child_ctx);
> >
> > /*
> > + * Clone itrace filters from the parent, if any
> > + */
> > + if (has_itrace_filter(child_event)) {
> > + if (perf_itrace_filters_clone(child_event, parent_event,
> > + child)) {
> > + put_ctx(child_ctx);
> > + free_event(child_event);
> > + return NULL;
>
> So inherit_event()'s return policy is somewhat opaque, there's 3
> possible returns:
>
> 1) a valid struct perf_event pointer; the clone was successful
> 2) ERR_PTR(err), the clone failed, abort inherit_group, fail fork()
> 3) NULL, the clone failed, ignore, continue
>
> We return NULL under two special cases:
>
> - the original event doesn't exist anymore, we're an orphan, do not make
> more orphans.
>
> - the parent event is dying
>
>
> I'm fairly sure this return should be in the 2) category. If we cannot
> fully clone the event something bad happened, we should not ignore it.
On second thought; we should not inherit the filters at all.
We should always use event->parent (if exists) for filters. Otherwise
inherited events will get different filters if you change the filter
after clone.
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