linux-kernel - Re: [PATCHv5 bpf-next 02/13] uprobe: Add support for session consumer

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Message-ID: <Zvv2eM2YNuiv7C8-@krava>
Date: Tue, 1 Oct 2024 15:17:44 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Oleg Nesterov <oleg@...hat.com>, 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@...ichev.me>, 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: [PATCHv5 bpf-next 02/13] uprobe: Add support for session consumer

On Mon, Sep 30, 2024 at 02:36:03PM -0700, Andrii Nakryiko wrote:
> On Sun, Sep 29, 2024 at 1:57 PM Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > This change allows the uprobe consumer to behave as session which
> > means that 'handler' and 'ret_handler' callbacks are connected in
> > a way that allows to:
> >
> >   - control execution of 'ret_handler' from 'handler' callback
> >   - share data between 'handler' and 'ret_handler' callbacks
> >
> > The session concept fits to our common use case where we do filtering
> > on entry uprobe and based on the result we decide to run the return
> > uprobe (or not).
> >
> > It's also convenient to share the data between session callbacks.
> >
> > To achive this we are adding new return value the uprobe consumer
> > can return from 'handler' callback:
> >
> >   UPROBE_HANDLER_IGNORE
> >   - Ignore 'ret_handler' callback for this consumer.
> >
> > And store cookie and pass it to 'ret_handler' when consumer has both
> > 'handler' and 'ret_handler' callbacks defined.
> >
> > We store shared data in the return_consumer object array as part of
> > the return_instance object. This way the handle_uretprobe_chain can
> > find related return_consumer and its shared data.
> >
> > We also store entry handler return value, for cases when there are
> > multiple consumers on single uprobe and some of them are ignored and
> > some of them not, in which case the return probe gets installed and
> > we need to have a way to find out which consumer needs to be ignored.
> >
> > The tricky part is when consumer is registered 'after' the uprobe
> > entry handler is hit. In such case this consumer's 'ret_handler' gets
> > executed as well, but it won't have the proper data pointer set,
> > so we can filter it out.
> >
> > Suggested-by: Oleg Nesterov <oleg@...hat.com>
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  include/linux/uprobes.h |  21 +++++-
> >  kernel/events/uprobes.c | 148 +++++++++++++++++++++++++++++++---------
> >  2 files changed, 137 insertions(+), 32 deletions(-)
> >
> 
> LGTM,
> 
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> 
> 
> Note also that I just resent the last patch from my patch set ([0]),
> hopefully it will get applied, in which case you'd need to do a tiny
> rebase.
> 
>   [0] https://lore.kernel.org/linux-trace-kernel/20240930212246.1829395-1-andrii@kernel.org/

the rebase is fine, but what I'm not clear about is that after yours and
Oleg's changes get in, my kernel changes will depend on peter's perf/core,
but bpf selftests changes will need bpf-next/master

jirka