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Date: Thu, 17 Aug 2017 07:39:26 -0700
From: Kees Cook <>
To: Thomas Gleixner <>
Cc: LKML <>, 
	"" <>
Subject: Re: refactoring timers to avoid init_timer*()

On Thu, Aug 17, 2017 at 7:30 AM, Thomas Gleixner <> wrote:
> On Wed, 16 Aug 2017, Kees Cook wrote:
>> In the process I noticed that we already have
>> scripts/coccinelle/api/setup_timer.cocci to detect existing cases of:
>> init_timer(t);
>> t->function = func;
>> t->data = data;
>> And replace it with: setup_timer(t, func, data);
>> Another pattern was:
>> t->expires = when;
>> add_timer(t);
>> Which can be replaced with mod_timer(t, when);
>> So, I've created scripts/coccinelle/api/mod_timer.cocci for the
>> latter, and done a few passes with manual review. The current result
>> doesn't fully eliminate init_timer() yet, but it gets much closer. I
>> just wanted to be sure that this whole clean-up would actually be
>> welcome before I try to nail down the last many cases.
> I think it's worth the trouble, but rather than having a gazillion of
> commits with the same changelog, we should do that based on a cocci script
> right before the next rc1 in one go and be done with it.
> That will cover most of the init_timer() cases and we can fixup the
> remaining few oddballs manually after that.

Okay, that sounds good. I'll work on improving the cocci scripts. For
example, I noticed that it doesn't notice having assignments _before_
the init_timer() call:

timer->function = func;
timer->data = data;

Whee. :)

BTW, I may back off on doing ->expires = when; add_timer(timer) -->
mod_timer(timer, when) changes since that actually removes a sanity
check in add_timer().

My plans currently are collapsing all the open-coded init_timer*()s
into setup_*timer() and then adding something like aim_timer(timer,
func, data) for post-setup function/data changes.


> I just noticed that we have the same pattern with hrtimer_init(). I had a
> stab on adding hrtimer_setup() and friends which takes a function argument
> and converted the bulk with coccinelle.
>     82 files changed, 186 insertions(+), 210 deletions(-)
> We can do that in the same sweep as the init_timer() one and then you can
> do the canary magic on hrtimers as well.
> Thanks,
>         tglx

Kees Cook
Pixel Security

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