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

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  [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload Jessica Yu <jeyu@redhat.com> - 2016-02-02 02:20 +0100
    Re: [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module  load and unload Jiri Kosina <jikos@kernel.org> - 2016-02-04 11:50 +0100
      Re: [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module  load and unload Steven Rostedt <rostedt@goodmis.org> - 2016-02-04 14:30 +0100
        Re: [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload Rusty Russell <rusty@rustcorp.com.au> - 2016-02-05 02:20 +0100

#1323692 — [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload

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@redhat.com

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@packer-debian-8-amd64.digitalocean.com


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

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#1326648 — Re: [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload

On Mon, 1 Feb 2016, 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.
> 
> Patches are based on linux-next.
> 
> v1 can be found here -
> http://lkml.kernel.org/g/1454049827-3726-1-git-send-email-jeyu@redhat.com
> 
> 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@packer-debian-8-amd64.digitalocean.com
> 
> 
> 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 +-----------

Steven, Rusty, what is your word on this please?

These two patches should be merged together, and I'd like to have the 
module patching issue Jessica discovered fixed for 4.5 still. IOW, if you 
Ack the parts relevant to you (ftrace and module), I'd be willing to take 
it to Linus through my tree.

Thanks,

-- 
Jiri Kosina
SUSE Labs

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#1326793 — Re: [PATCH v2 0/2] Fix ordering of ftrace/livepatch calls on module load and unload

On Thu, 4 Feb 2016 11:43:57 +0100 (CET)
Jiri Kosina <jikos@kernel.org> wrote:

>
> Steven, Rusty, what is your word on this please?

I'm fine with the first patch, but you still need an Ack from Rusty on
both. Unfortunately, Rusty is more part-time on kernel development
these days. Hopefully he's still paying attention.

> 
> These two patches should be merged together, and I'd like to have the 
> module patching issue Jessica discovered fixed for 4.5 still. IOW, if you 
> Ack the parts relevant to you (ftrace and module), I'd be willing to take 
> it to Linus through my tree.

If you get Rusty's acks, you can add my:

 Reviewed-by: Steven Rostedt <rostedt@goodmis.org>

on the first patch and take it through your tree.

-- Steve

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#1327387

Steven Rostedt <rostedt@goodmis.org> writes:
>> These two patches should be merged together, and I'd like to have the 
>> module patching issue Jessica discovered fixed for 4.5 still. IOW, if you 
>> Ack the parts relevant to you (ftrace and module), I'd be willing to take 
>> it to Linus through my tree.
>
> If you get Rusty's acks, you can add my:
>
>  Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
>
> on the first patch and take it through your tree.

Agreed.

Acked-by: Rusty Russell <rusty@rustcorp.com.au> (module.c parts)

Cheers,
Rusty.

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