Re: Fix ordering of ftrace/livepatch calls on module load and unload

[Jessica Yu]

+++ Josh Poimboeuf [08/02/16 11:48 -0600]:
> On Fri, Feb 05, 2016 at 10:08:15PM -0500, Jessica Yu wrote:
> > 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.
>
> Since Rusty agreed to your suggested changes for splitting up
> complete_formation() and for setting mod->state = MODULE_STATE_GOING
> before calling the going notifiers in the error path, can you do a v4
> with those changes?  They should probably be split up like:
>
> 1. split up complete_formation()
> 2. set MODULE_STATE_GOING before calling going notifiers in error path
> 3. remove ftrace module notifier
> 4. remove livepatch module notifier

Sure, I'll do that.

Jessica