[PATCH v2 0/5] tracing/user_events: Add auto cleanup and a flag to persist events

Beau Belgrave
2023-06-05T23:39:08Z

As part of the discussions for user_events aligning to be used with eBPF
it became clear [1] we needed a way to delete events without having to rely
upon the delete IOCTL. Steven suggested that we simply have an owner
for the event, however, the event can be held by more than just the
first register FD, such as perf/ftrace or additional registers. In order
to handle all those cases, we must only delete after all references are
gone from both user and kernel space.

This series adds a new register flag, USER_EVENT_REG_PERSIST, which
causes the event to not delete itself upon the last put reference. We
cannot fully drop the delete IOCTL, since we still want to enable events to
be registered early via dynamic_events and persist. Events that do not use
this new flag are auto-cleaned up upon no longer being used.

NOTE: I'll need to merge this work once we take these [2] [3] patches
into for-next. I'm happy to do so once they land there.

1: https://lore.kernel.org/linux-trace-kernel/20230518093600.3f119d68@rorschach.local.home/
2: https://lore.kernel.org/linux-trace-kernel/20230529032100.286534-1-sunliming@kylinos.cn/
3: https://lore.kernel.org/linux-trace-kernel/20230519230741.669-1-beaub@linux.microsoft.com/

Change history

v2:
Renamed series to "Add auto cleanup and a flag to persist events"
Changed auto-delete to be default behavior, with new flag to persist events

Beau Belgrave (5):
tracing/user_events: Store register flags on events
tracing/user_events: Track refcount consistently via put/get
tracing/user_events: Add auto cleanup and a flag to persist events
tracing/user_events: Add self-test for persist flag
tracing/user_events: Add persist flag documentation

Documentation/trace/user_events.rst | 21 +-
include/uapi/linux/user_events.h | 10 +-
kernel/trace/trace_events_user.c | 184 ++++++++++++++----
.../testing/selftests/user_events/abi_test.c | 144 +++++++++++++-
.../selftests/user_events/ftrace_test.c | 1 +
5 files changed, 309 insertions(+), 51 deletions(-)

base-commit: 3862f86c1529fa0016de6344eb974877b4cd3838
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2.25.1