hi,
while adding test for pinning the module while there's
trampoline attach to it, I noticed that we don't allow
link detach and following re-attach for trampolines.

I'm not sure this was on purpose, but seems as natural
use of the interface, although the only user is the test
for now.

You need to have patch [1] from bpf tree for test module
attach test to pass.

thanks,
jirka


[1] https://lore.kernel.org/bpf/20210326105900.151466-1-jolsa@kernel.org/ (local)
---
Jiri Olsa (4):
      bpf: Allow trampoline re-attach
      selftests/bpf: Add re-attach test to fentry_test
      selftests/bpf: Add re-attach test to fexit_test
      selftests/bpf: Test that module can't be unloaded with attached trampoline

 kernel/bpf/syscall.c                                   | 25 +++++++++++++++++++------
 kernel/bpf/trampoline.c                                |  2 +-
 tools/testing/selftests/bpf/prog_tests/fentry_test.c   | 58 +++++++++++++++++++++++++++++++++++++++++++++-------------
 tools/testing/selftests/bpf/prog_tests/fexit_test.c    | 58 +++++++++++++++++++++++++++++++++++++++++++++-------------
 tools/testing/selftests/bpf/prog_tests/module_attach.c | 23 +++++++++++++++++++++++
 5 files changed, 133 insertions(+), 33 deletions(-)