[PATCH v4 0/4] 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:
https://lkml.kernel.org/g/1454049827-3726-1-git-send-email-jeyu@xxxxxxxxxx
v2:
https://lkml.kernel.org/g/1454375856-27757-1-git-send-email-jeyu@xxxxxxxxxx
v3:
https://lkml.kernel.org/g/1454728097-7106-1-git-send-email-jeyu@xxxxxxxxxx

v4:
- Split part of complete_formation() into prepare_coming_module() to make
  error handling a bit easier
- Minor tweak: change mod->state to going before calling going notifiers in
  the load_module error path
- Swapped out obj->mod = NULL assignment in klp_module_coming() for a
  call to klp_free_object_loaded()

v3:
- Fix incorrect comments
- Rename klp_module_{enable,disable} to klp_module_{coming,going}
- Remove externs from livepatch.h
- Fix error handling in kernel/module.c

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 (4):
  modules: split part of complete_formation() into
    prepare_coming_module()
  modules: set mod->state to MODULE_STATE_GOING before going notifiers
    are called
  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   | 145 ++++++++++++++++++++++------------------------
 kernel/module.c           |  40 ++++++++++---
 kernel/trace/ftrace.c     |  36 +-----------
 5 files changed, 116 insertions(+), 120 deletions(-)

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2.4.3