Re: [PATCH v2] perf: Synchronously cleanup child events

[Peter Zijlstra]

On Fri, Jan 22, 2016 at 11:44:03AM -0800, Alexei Starovoitov wrote:
> On Fri, Jan 22, 2016 at 01:38:47PM +0100, Peter Zijlstra wrote:
> > On Fri, Jan 22, 2016 at 01:35:40PM +0200, Alexander Shishkin wrote:
> > > Peter Zijlstra <peterz@xxxxxxxxxxxxx> writes:
> > > 
> > > > So I think there's a number of problems still :-(
> 
> I've been looking at how perf_event->owner is handled and couldn't
> figure out how you deal with the case of passing perf_event_fd via scm_rights.
> It seems one process can open an event, pass it to another process,
> but when current process exists owner will still point to dead task,
> since refcount > 0.
> Which part am I missing?

Nothing, you raised a good point. I think this shows we cannot link
!event->owner to an event being 'dead'.

If we keep these two states separate, the scm_rights thing should work
again.