Re: SMP BUG

[Andrew Morton <akpm@osdl.org>]

Russell King <rmk+lkml@arm.linux.org.uk> wrote:
>
> On Wed, Feb 15, 2006 at 03:30:13PM -0800, Andrew Morton wrote:
> > Linus Torvalds <torvalds@osdl.org> wrote:
> > > That said, nobody seemed to comment on this patch by Rik, which seemed to 
> > >  be a nice cleanup regardless of any other issues.
> > 
> > I thought that patch wasn't a good one.  The runqueues should be
> > initialised in sched_init().  init_idle() is called from fork_idle() which
> > is called from the bowels of arch code.  I'm not sure that it gets called
> > at all if !SMP (which seems strange).
> 
> Wouldn't it make sense to do this initialisation in a CPU_UP_PREPARE
> notifier, if not already done?
> 

Could be - we have a couple of notifier handlers in sched.c already,
although they're inside awkward CONFIG_* wrappers.

But architectures need to initialise cpu_possible_map in setup_arch()
anyway, because we immediately call setup_per_cpu_areas(), which needs to
know which CPUs are possible so it will only allocate memory for them.

Yes, architectures can override the generic setup_per_cpu_areas(), but the
same argument applies: they don't want to be allocating memory for
!possible CPUs.

So I think it's sanest to say that the arch shalt initialise cpu_possible_map
in setup_arch().