Merge branch 'trampoline-fixes'

Jiri Olsa says:

====================
hi,
sending 2 fixes to fix kernel support for loading
trampoline programs in bcc/bpftrace and allow to
unwind through trampoline/dispatcher.

Original rfc post [1].

Speedup output of perf bench while running klockstat.py
on kprobes vs trampolines:

    Without:
            $ perf bench sched messaging -l 50000
            ...
                 Total time: 18.571 [sec]

    With current kprobe tracing:
            $ perf bench sched messaging -l 50000
            ...
                 Total time: 183.395 [sec]

    With kfunc tracing:
            $ perf bench sched messaging -l 50000
            ...
                 Total time: 39.773 [sec]

v4 changes:
  - rebased on latest bpf-next/master
  - removed image tree mutex and use trampoline_mutex instead
  - checking directly for string pointer in patch 1 [Alexei]
  - skipped helpers patches, as they are no longer needed [Alexei]

v3 changes:
  - added ack from John Fastabend for patch 1
  - move out is_bpf_image_address from is_bpf_text_address call [David]

v2 changes:
  - make the unwind work for dispatcher as well
  - added test for allowed trampolines count
  - used raw tp pt_regs nest-arrays for trampoline helpers

thanks,
jirka

[1] https://lore.kernel.org/netdev/20191229143740.29143-1-jolsa@kernel.org/
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>