linux-kernel - Re: [PATCH 05/10] perf/uprobe: SRCU-ify uprobe->consumer list

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Message-ID: <20240709133349.GC28495@redhat.com>
Date: Tue, 9 Jul 2024 15:33:49 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: mingo@...nel.org, andrii@...nel.org, linux-kernel@...r.kernel.org,
	rostedt@...dmis.org, mhiramat@...nel.org, jolsa@...nel.org,
	clm@...a.com, paulmck@...nel.org
Subject: Re: [PATCH 05/10] perf/uprobe: SRCU-ify uprobe->consumer list

On 07/09, Peter Zijlstra wrote:
>
> > +	guard(srcu)(&uprobes_srcu);
> > +
> > +	for_each_consumer_rcu(uc, uprobe->consumers) {
> >  		int rc = 0;
> >
> >  		if (uc->handler) {
> > @@ -2116,7 +2126,6 @@ static void handler_chain(struct uprobe
> >  		WARN_ON(!uprobe_is_active(uprobe));
> >  		unapply_uprobe(uprobe, current->mm);
>
>    ^^^ this remove case needs more thought.

Yeah... that is why the current code doesn't use ->consumer_rwsem, iirc.

And consumer_add/del need some changes. Say, consumer_add() does

	uc->next = uprobe->consumers;
	uprobe->consumers = uc;

I guess it should do

	WRITE_ONCE(uc->next, uprobe->consumers);
	rcu_assign_pointer(uprobe->consumers, uc);

Oleg.