[GIT PULL] ftrace: Updates for 7.3

Linus,

ftrace updates for 7.3:

- Deprecate ftrace_enabled in disabling ftrace

  The file /proc/sys/kernel/ftrace_enabled was created when ftrace was first
  introduced back in 2008. It was to be a "kill switch" if something was to
  go wrong. It was also used as a way to turn off function tracing for the
  latency tracers that would have it on by default. But in 2013 (Linux 3.10)
  the option "function-trace" was introduced to disable function tracing for
  the latency tracers as the "ftrace_enabled" file was considered too big of
  a hammer and caused too many side effects.

  When live kernel patching came along, disabling ftrace via the
  ftrace_enabled file would put the system into an unstable state if a live
  kernel patch was installed. This created the need to mark some function
  hooks as "PERMANENT".

  Now there's a need for BPF usage marked as PERMANENT for the same reasons.

  The file "ftrace_enabled" usage is no longer viable. It doesn't do what it
  says it does and there is no reason to use it.

  Make writing '0' to it a nop and print a message saying its usage is
  deprecated. The return value of writing '0' is -EOPNOTSUPP so that user
  space will error on that write (hopefully to inform any developer that it
  no longer works).

  Eventually the file should be removed completely, but for now just making
  it not do anything is the path forward to that.

- Update the livepatch tests to handle ftrace_enabled being disabled

  Because in the past, livepatch was broken by ftrace_enabled being turned
  off, there's a test case that checks to make sure it still doesn't break.
  But having the write of '0' return an error caused that test to break.
  Updated the test to handle the new change.


Please pull the latest ftrace-v7.3 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace.git
ftrace-v7.3

Tag SHA1: bbc5fbe8256ea1deaa8708d0887a97e594155ce6
Head SHA1: 88b3e7fedc07d940c32eb5c0733a780e944b6b47


Andrey Grodzovsky (2):
      ftrace: deprecate disabling via ftrace_enabled sysctl
      selftests/livepatch: update test-ftrace.sh for deprecated ftrace_enabled

----
 Documentation/trace/ftrace.rst                   |  5 +++
 kernel/trace/ftrace.c                            | 43 ++++------------------
 tools/testing/selftests/livepatch/functions.sh   | 14 ++++++++
 tools/testing/selftests/livepatch/test-ftrace.sh | 45 +++++++++++++++---------
 4 files changed, 53 insertions(+), 54 deletions(-)
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