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

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Message-ID: <CAEf4BzZ+1=YU=61mVup8pAc80SOvNuYtMzNdz4miH+Sm4qV4ig@mail.gmail.com>
Date: Mon, 30 Sep 2024 14:36:03 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jiri Olsa <jolsa@...nel.org>
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 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/


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