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

LGTM,

Acked-by: Andrii Nakryiko <andrii@kernel.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/ (local)


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