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

[Andrii Nakryiko]

On Sun, Sep 29, 2024 at 1:57 PM Jiri Olsa <jolsa@xxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
>  include/linux/uprobes.h |  21 +++++-
>  kernel/events/uprobes.c | 148 +++++++++++++++++++++++++++++++---------
>  2 files changed, 137 insertions(+), 32 deletions(-)
>

LGTM,

Acked-by: Andrii Nakryiko <andrii@xxxxxxxxxx>


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@xxxxxxxxxx/


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