Re: [RFC PATCH v3 4/7] powerpc: regain entire stack space

[Christophe LEROY]

Le 03/10/2018 Ã 09:07, Nicholas Piggin a ÃcritÂ:
> On Wed, 3 Oct 2018 08:45:25 +0200
> Christophe LEROY <christophe.leroy@xxxxxx> wrote:
>
> > Le 03/10/2018 Ã 08:30, Nicholas Piggin a ÃcritÂ:
> > > On Wed, 3 Oct 2018 07:52:59 +0200
> > > Christophe LEROY <christophe.leroy@xxxxxx> wrote:
> > >    
> > > > Le 03/10/2018 Ã 07:34, Nicholas Piggin a ÃcritÂ:
> > > > > On Mon,  1 Oct 2018 12:30:25 +0000 (UTC)
> > > > > Christophe Leroy <christophe.leroy@xxxxxx> wrote:
> > > > >       
> > > > > > thread_info is not anymore in the stack, so the entire stack
> > > > > > can now be used.
> > > > >
> > > > > Nice.
> > > > >       
> > > > > > In the meantime, all pointers to the stacks are not anymore
> > > > > > pointers to thread_info so this patch changes them to void*
> > > > >
> > > > > Wasn't this previously effectively already the case with patch
> > > > > 3/7? You had thread_info sized space left there, but it was not
> > > > > used or initialized right? Does it make sense to move this part
> > > > > of it to the previous patch?
> > > >
> > > > Not really.
> > > >
> > > > In 3/7 I changed the prototypes of two functions that really used the
> > > > pointer as a task pointer only.
> >
> > I meant 2/7 here sorry.
> >
> > > > Here it change things that before 4/7 were really used as both stack
> > > > pointers and thread_info pointers.
> >
> > And here I meant 3/7
> >
> > > What uses it as a thread_info pointer? It seems more like a stack
> > > with some amount of unused space in it but that's all.
> >
> > Before 3/7, we have
> >
> > void do_softirq_own_stack(void)
> > {
> > 	struct thread_info *curtp, *irqtp;
> >
> > 	curtp = current_thread_info();
> > 	irqtp = softirq_ctx[smp_processor_id()];
> > 	irqtp->task = curtp->task;
> > 	irqtp->flags = 0;
> > 	call_do_softirq(irqtp);
> > 	irqtp->task = NULL;
> >
> > 	/* Set any flag that may have been set on the
> > 	 * alternate stack
> > 	 */
> > 	if (irqtp->flags)
> > 		set_bits(irqtp->flags, &curtp->flags);
> > }
> >
> > After 3/7, we have
> >
> >    void do_softirq_own_stack(void)
> >    {
> > 	struct thread_info *irqtp;
> >
> >    	irqtp = softirq_ctx[smp_processor_id()];
> >    	call_do_softirq(irqtp);
> >    }
> >
> >
> > So now only we can change irqtp to void* can't we ?
>
> In patch 3 we can, right? That's what I mean by moving from
> thread_info * to void * in patch 3 rather than 4.

Ah ok, that's what you meant. Sorry.

> But if you prefer not to, it's fine. Maybe it keeps patch 3
> a little smaller.

Yes indeed, that's the idea, keep patch 3 to the strict minimum and do 
cleanups afterwards.

Christophe

> Thanks,
> Nick