Re: perf: FORMAT_GROUP on attached process stops working in 3.16-rc

From: Peter Zijlstra
Date: Tue Jul 15 2014 - 10:38:36 EST

On Tue, Jul 15, 2014 at 10:36:33AM -0400, Vince Weaver wrote:
> Hello
> I noticed in the 3.16-rc kernels that one of my regression tests was
> failing, specifically
> This test creates an event group with two events and PERF_FORMAT_GROUP
> set.
> It creates a child process, stops it, attaches the event group to it,
> starts the events and the child, waits for the child to finish, stops the
> events, then reads the value.
> In theory a subsequent read from the group leader should return values for
> *both* events (due to PERF_FORMAT_GROUP) but this stopped working, it only
> returns the value for the leader.
> I've bisected it down to change: 15a2d4de0eab5
> "perf: Always destroy groups on exit"
> So is this expected behavior due to this patch, or is it a regression?

Regression, lemme try and wrap my head around it. Thanks!

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