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[v2,bpf-next,0/2] bpf: fix use of trace_printk() in BPF

Message ID 1594390953-31757-1-git-send-email-alan.maguire@oracle.com
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Series bpf: fix use of trace_printk() in BPF | expand

Message

Alan Maguire July 10, 2020, 2:22 p.m. UTC 
Steven suggested a way to resolve the appearance of the warning banner
that appears as a result of using trace_printk() in BPF [1].
Applying the patch and testing reveals all works as expected; we
can call bpf_trace_printk() and see the trace messages in
/sys/kernel/debug/tracing/trace_pipe and no banner message appears.

Also add a test prog to verify basic bpf_trace_printk() helper behaviour.

Changes since v1:

- reorder header inclusion in bpf_trace.c (Steven, patch 1)
- trace zero-length messages also (Andrii, patch 1)
- use a raw spinlock to ensure there are no issues for PREMMPT_RT
  kernels when using bpf_trace_printk() within other raw spinlocks
  (Steven, patch 1)
- always enable bpf_trace_printk() tracepoint when loading programs
  using bpf_trace_printk() as this will ensure that a user disabling
  that tracepoint will not prevent tracing output from being logged
  (Steven, patch 1)
- use "tp/raw_syscalls/sys_enter" and a usleep(1) to trigger events
  in the selftest ensuring test runs faster (Andrii, patch 2)

[1]  https://lore.kernel.org/r/20200628194334.6238b933@oasis.local.home

Alan Maguire (2):
  bpf: use dedicated bpf_trace_printk event instead of trace_printk()
  selftests/bpf: add selftests verifying bpf_trace_printk() behaviour

 kernel/trace/Makefile                              |  2 +
 kernel/trace/bpf_trace.c                           | 41 ++++++++++--
 kernel/trace/bpf_trace.h                           | 34 ++++++++++
 .../selftests/bpf/prog_tests/trace_printk.c        | 74 ++++++++++++++++++++++
 tools/testing/selftests/bpf/progs/trace_printk.c   | 21 ++++++
 5 files changed, 167 insertions(+), 5 deletions(-)
 create mode 100644 kernel/trace/bpf_trace.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/trace_printk.c
 create mode 100644 tools/testing/selftests/bpf/progs/trace_printk.c