Re: [PATCH 0/3] tracing/user_events: Allow events to persist for perfmon_capable users

[Steven Rostedt]

Hi Beau,

Just an FYI, except for fixes, it is never a good ideal to send out patches
while the merge window is open. They will likely be ignored for the
entirety of the merge window.

-- Steve


On Fri,  1 Sep 2023 20:43:29 +0000
Beau Belgrave <beaub@xxxxxxxxxxxxxxxxxxx> wrote:

> There are several scenarios that have come up where having a user_event
> persist even if the process that registered it exits. The main one is
> having a daemon create events on bootup that shouldn't get deleted if
> the daemon has to exit or reload. Another is within OpenTelemetry
> exporters, they wish to potentially check if a user_event exists on the
> system to determine if exporting the data out should occur. The
> user_event in this case must exist even in the absence of the owning
> process running (such as the above daemon case).
> 
> Since persistent events aren't automatically cleaned up, we want to ensure
> only trusted users are allowed to do this. It seems reasonable to use
> CAP_PERFMON as that boundary, since those users can already do many things
> via perf_event_open without requiring full CAP_SYS_ADMIN.
> 
> This patchset brings back the ability to use /sys/kernel/tracing/dynamic_events
> to create user_events, as persist is now back to being supported. Both the
> register and delete of events that persist require CAP_PERFMON, which prevents
> a non-perfmon user from making an event go away that a perfmon user decided
> should persist.
> 
> Beau Belgrave (3):
>   tracing/user_events: Allow events to persist for perfmon_capable users
>   selftests/user_events: Test persist flag cases
>   tracing/user_events: Document persist event flags
> 
>  Documentation/trace/user_events.rst           | 21 ++++++-
>  include/uapi/linux/user_events.h              | 11 +++-
>  kernel/trace/trace_events_user.c              | 28 +++++-----
>  .../testing/selftests/user_events/abi_test.c  | 55 ++++++++++++++++++-
>  .../testing/selftests/user_events/dyn_test.c  | 54 +++++++++++++++++-
>  5 files changed, 149 insertions(+), 20 deletions(-)
> 
> 
> base-commit: f940e482b0f889e697372a22b6c15da87aa1f63a