Re: [PATCH] debugobjects: Move printk out of db lock critical sections

[Dmitry Safonov]

On Thu, 13 Dec 2018 at 05:19, Sergey Senozhatsky
<sergey.senozhatsky.work@xxxxxxxxx> wrote:
>
> On (12/13/18 04:35), Dmitry Safonov wrote:
> > I've tried to review it and found minor issues like missed
> > debug_object_is_on_stack() for initializing already active object.
> >
> > But than I come to opinion that it's just generally unsafe:
> > debug_obj life-time is protected by bucket's spin_lock.
> > Check the conditions when free_object() is being called.
>
> I thought about it for a second, but couldn't figure out if this race
> was real.
>
> E.g. uart case - if there are two paths which concurrently free and
> access debug object, then the same race condition should exist for
> the xmit.buf page. debug object's lifespan should be the same as the
> lifespan of, ummm, whatever the thing that debug object is attached
> to? I'm surely missing something here.

I think the point of debugobjects is to reduce the damage caused
by an improper life-time of objects.

IIUC:
1. alloc_page()
2. dynamically allocate a workqueue on a new page
3. schedule some work
4. until the work has run free_page()

So, wroqueue fixup upon freeing should cancel the work TBD.

But maybe I've misunderstood something..
And it's 6 am in my timezone, I'll catch some sleep and
will glance this with some morning coffee.

Thanks,
             Dmitry