BACKPORT: bpf: permit multiple bpf attachments for a single perf event

This patch enables multiple bpf attachments for a
kprobe/uprobe/tracepoint single trace event.
Each trace_event keeps a list of attached perf events.
When an event happens, all attached bpf programs will
be executed based on the order of attachment.

A global bpf_event_mutex lock is introduced to protect
prog_array attaching and detaching. An alternative will
be introduce a mutex lock in every trace_event_call
structure, but it takes a lot of extra memory.
So a global bpf_event_mutex lock is a good compromise.

The bpf prog detachment involves allocation of memory.
If the allocation fails, a dummy do-nothing program
will replace to-be-detached program in-place.

Signed-off-by: Yonghong Song <yhs@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit e87c6bc3852b981e71c757be20771546ce9f76f3)
Signed-off-by: Connor O'Brien <connoro@google.com>
Bug: 121213201
Bug: 138317270
Test: build & boot cuttlefish; attach 2 progs to 1 tracepoint
Change-Id: I390d8c0146888ddb1aed5a6f6e5dae7ef394ebc9