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

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Message-ID: <20250604155949.GK39944@noisy.programming.kicks-ass.net>
Date: Wed, 4 Jun 2025 17:59:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Leo Yan <leo.yan@....com>
Cc: Yeoreum Yun <yeoreum.yun@....com>, mingo@...hat.com, mingo@...nel.org,
	acme@...nel.org, namhyung@...nel.org, mark.rutland@....com,
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
	irogers@...gle.com, adrian.hunter@...el.com,
	kan.liang@...ux.intel.com, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, David Wang <00107082@....com>
Subject: Re: [PATCH 1/1] perf/core: fix dangling cgroup pointer in cpuctx

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 :-(