[PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload

[Jessica Yu]

As explained here [1], livepatch modules are failing to initialize properly
because the ftrace coming module notifier (which calls
ftrace_module_enable()) runs *after* the livepatch module notifier (which
enables the patch(es)). Thus livepatch attempts to apply patches to
modules before ftrace_module_enable() is even called for the corresponding
module(s). As a result, patch modules break. Ftrace code must run before
livepatch on module load, and the reverse is true on module unload.

For ftrace and livepatch, order of initialization (plus exit/cleanup code)
is important for loading and unloading modules, and using module notifiers
to perform this work is not ideal since it is not always clear what gets
called when. In this patchset, dependence on the module notifier call chain
is removed in favor of hard coding the corresponding function calls in the
module loader. This promotes better code visibility and ensures that ftrace
and livepatch code get called in the correct order on patch module load and
unload.

Tested the changes with a test livepatch module that patches 9p and nilfs2,
and verified that the issue described in [1] is fixed.

Patches are based on linux-next.

v1 can be found here -
http://lkml.kernel.org/g/1454049827-3726-1-git-send-email-jeyu@xxxxxxxxxx

v2:
- Instead of splitting the ftrace and livepatch notifiers into coming + going
  notifiers and adjusting their priorities, remove ftrace and livepatch notifiers
  completely and hard-code the necessary function calls in the module loader.

[1] http://lkml.kernel.org/g/20160128204033.GA32131@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


Jessica Yu (2):
  ftrace/module: remove ftrace module notifier
  livepatch/module: remove livepatch module notifier

 include/linux/ftrace.h    |   6 +-
 include/linux/livepatch.h |   9 +++
 kernel/livepatch/core.c   | 144 ++++++++++++++++++++++------------------------
 kernel/module.c           |  12 ++++
 kernel/trace/ftrace.c     |  36 +-----------
 5 files changed, 95 insertions(+), 112 deletions(-)

-- 
2.4.3