linux-kernel - Re: [PATCH 19/19] perf: Make perf_pmu

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Message-ID: <20241105151651.GI10375@noisy.programming.kicks-ass.net>
Date: Tue, 5 Nov 2024 16:16:51 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: mingo@...nel.org, lucas.demarchi@...el.com,
	linux-kernel@...r.kernel.org, willy@...radead.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
Subject: Re: [PATCH 19/19] perf: Make perf_pmu_unregister() useable

On Tue, Nov 05, 2024 at 10:08:54AM -0500, Liang, Kan wrote:
> > @@ -2427,6 +2429,7 @@ __perf_remove_from_context(struct perf_e
> >  			   void *info)
> >  {
> >  	struct perf_event_pmu_context *pmu_ctx = event->pmu_ctx;
> > +	enum perf_event_state state = PERF_EVENT_STATE_OFF;
> 
> Set the PERF_EVENT_STATE_OFF as default seems dangerous.
> If the event was in an error state, the state will be overwritten to the
> PERF_EVENT_STATE_OFF later.
> 
> One example may be the perf_pmu_migrate_context(). After the migration,
> it looks like all the error state will be cleared.
> 
> Thanks,
> Kan
> 
> >  	unsigned long flags = (unsigned long)info;
> >  
> >  	ctx_time_update(cpuctx, ctx);
> > @@ -2435,16 +2438,22 @@ __perf_remove_from_context(struct perf_e
> >  	 * Ensure event_sched_out() switches to OFF, at the very least
> >  	 * this avoids raising perf_pending_task() at this time.
> >  	 */
> > -	if (flags & DETACH_DEAD)
> > +	if (flags & DETACH_EXIT)
> > +		state = PERF_EVENT_STATE_EXIT;
> > +	if (flags & DETACH_REVOKE)
> > +		state = PERF_EVENT_STATE_REVOKED;
> > +	if (flags & DETACH_DEAD) {
> >  		event->pending_disable = 1;
> > +		state = PERF_EVENT_STATE_DEAD;
> > +	}
> >  	event_sched_out(event, ctx);
> >  	if (flags & DETACH_GROUP)
> >  		perf_group_detach(event);
> >  	if (flags & DETACH_CHILD)
> >  		perf_child_detach(event);
> >  	list_del_event(event, ctx);
> > -	if (flags & DETACH_DEAD)
> > -		event->state = PERF_EVENT_STATE_DEAD;
> > +
> > +	event->state = state;

How about we make this:

	event->state = min(event->state, state);

?