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SubjectRe: [patch 0/6] rcu head debugobjects
On Sun, Mar 28, 2010 at 04:07:10AM +0200, Thomas Gleixner wrote:
> B1;2005;0cOn Sat, 27 Mar 2010, Paul E. McKenney wrote:
> >
> > o Patch 4/6 looks good to me, and given that Thomas hasn't
> > complained, I am guessing that he is OK with it.
>
> Looks sane at the first glance. Will go over it in detail tomorrow.
>
> > o Patch 6/6: Would it be possible to use the object_is_on_stack()
> > function defined in include/linux/sched.h instead of passing
> > in the flag on_stack to bdi_work_init()? It looks like
> > fs/fs-writeback.c already includes include/linux/sched.h, so
> > shouldn't be a problem from a #include-hell viewpoint.
>
> Well, I'm a bit wary about that. The reason is that we really want
> the annotation of:
>
> init_on_stack();
> ....
> destroy_on_stack();
>
> instead of the confusing:
>
> init();
> ....
> destroy_on_stack();
>
> So having an automatism in the bdi_work_init() function will people
> make forget to put the destroy_on_stack() annotation into it.
>
> The flag is horrible as well. How about this:
>
> /* helper function, do not use in code ! */
> __bdi_work_init(....., onstack)
> {
> ....
> if (on_stack) {
> work.state |= WS_ONSTACK;
> init_rcu_head_on_stack(&work.rcu_head);
> } else {
> ....
> }
>
> See, how this moves also the "work.state |= WS_ONSTACK;" line out of
> the calling code.
>
> bdi_work_init(...)
> {
> __bdi_work_init(...., false);
> }
>
> bdi_work_init_on_stack(...)
> {
> __bdi_work_init(...., true);
> }
>
>
> out of the code.
>
> To make it complete, please do not use the asymmetric:
>
> destroy_rcu_head_on_stack(&work.rcu_head);
>
> Create a helper function:
>
> bdi_destroy_work_on_stack(...)
> {
> destroy_rcu_head_on_stack(work->rcu_head);
> }
>
> That makes it way more readable and we did that with the other on
> stack initializers as well.

Hello, Thomas,

I must defer to you on this one. ;-)

Thanx, Paul


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