linux-kernel - Re: [RFC bpf-next 01/10] uprobe: Add session callbacks to uprobe

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Message-ID: <20240605160117.GE25006@redhat.com>
Date: Wed, 5 Jun 2024 18:01:17 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
	Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...omium.org>,
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC bpf-next 01/10] uprobe: Add session callbacks to
 uprobe_consumer

On 06/05, Oleg Nesterov wrote:
>
> > +/*
> > + * Make sure all the uprobe consumers have only one type of entry
> > + * callback registered (either handler or handler_session) due to
> > + * different return value actions.
> > + */
> > +static int consumer_check(struct uprobe_consumer *curr, struct uprobe_consumer *uc)
> > +{
> > +	if (!curr)
> > +		return 0;
> > +	if (curr->handler_session || uc->handler_session)
> > +		return -EBUSY;
> > +	return 0;
> > +}
>
> Hmm, I don't understand this code, it doesn't match the comment...
>
> The comment says "all the uprobe consumers have only one type" but
> consumer_check() will always fail if the the 1st or 2nd consumer has
> ->handler_session != NULL ?
>
> Perhaps you meant
>
> 	if (!!curr->handler != !!uc->handler)
> 		return -EBUSY;
>
> ?

OK, the changelog says

	Which means that there can be only single user of a uprobe (inode +
	offset) when session consumer is registered to it.

so the code is correct. But I still think the comment is misleading.

Oleg.