Re: [PATCH 1/1] perf/core: fix dangling cgroup pointer in cpuctx

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Jun 04, 2025 at 04:46:39PM +0100, Leo Yan wrote:
> On Wed, Jun 04, 2025 at 04:16:40PM +0200, Peter Zijlstra wrote:
> 
> [...]
> 
> > It might be prudent to do something like so:
> 
> Thanks for the patch.
> 
> > +static void __event_disable(struct perf_event *event,
> > +			    struct perf_event_context *ctx,
> > +			    enum perf_event_state state)
> > +{
> > +	if (event == event->group_leader)
> > +		group_sched_out(event, ctx);
> 
> I am a bit struggle for this code line. It disables all events in a
> group, but only clear cgroup pointer for group leader but miss to clear
> for sibling events.
> 
> If the cgroup pointer is only used for group leader, maybe we only
> maintain (set and clear) the cgroup pointer for the leader?

Hmm, so yeah, that is weird indeed.

So perf_cgroup_event_enable() is called in list_add_event(), which is
perf_install_in_context() and that should be every single event.

So yeah, I'm thinking we're having more bugs here still :-(