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From: Jiri Olsa <olsajiri@gmail.com>
Date: Wed, 5 Jun 2024 22:18:55 +0200
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, bpf@vger.kernel.org,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org
Subject: Re: [RFC bpf-next 01/10] uprobe: Add session callbacks to
 uprobe_consumer
Message-ID: <ZmDIL85R_P8NhIwm@krava>
References: <20240604200221.377848-1-jolsa@kernel.org>
 <20240604200221.377848-2-jolsa@kernel.org>
 <20240605152457.GD25006@redhat.com>
 <20240605160117.GE25006@redhat.com>
 <20240605163624.GG25006@redhat.com>
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On Wed, Jun 05, 2024 at 06:36:25PM +0200, Oleg Nesterov wrote:
> On 06/05, Oleg Nesterov wrote:
> >
> > 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.
> 
> Cough... perhaps it is correct but I am still confused even we forget about
> the comment ;)
> 
> OK, uprobe can have a single consumer with ->handler_session != NULL. I guess
> this is because return_instance->data is "global".
> 
> So uprobe can have multiple handler_session == NULL consumers before
> handler_session != NULL, but not after ?

ah yea it should have done what's in the comment, so it's missing
the check for handler.. session handlers are meant to be exclusive

thanks,
jirka