Merge branch 'bpf-permit-multiple-bpf-attachments-for-a-single-perf-tracepoint-event'

Yonghong Song says:

====================
bpf: permit multiple bpf attachments for a single perf tracepoint event

This patch set adds support to permit multiple bpf prog attachments
for a single perf tracepoint event. Patch 1 does some cleanup such
that perf_event_{set|free}_bpf_handler is called under the
same condition. Patch 2 has the core implementation, and
Patch 3 adds a test case.

Changelogs:
v2 -> v3:
  . fix compilation error.
v1 -> v2:
  . fix a potential deadlock issue discovered by Daniel.
  . fix some coding style issues.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>