Re: [patch] Re: 2.6.16-rc4-mm1 (bugs and lockups)

[Andrew Morton <akpm@osdl.org>]

Stas Sergeev <stsp@aknet.ru> wrote:
>
> main.c: moved smp_prepare_boot_cpu() call earlier. This
>  was necessary because otherwise printk() can't print
>  It checks cpu_online(), which returns false. This change
>  is consistent with the UP case, where's the boot CPU is
>  "online" from the very beginning, AFAICS. But again, I am
>  not entirely sure whether this is safe.
> 

Yeah, this is scary.  Early boot is fragile and complex and architectures
might not expect to run smp_prepare_boot_cpu() before setup_arch().

umm, actually it's wrong.  i386's smp_prepare_boot_cpu() diddles with
per-cpu memory, and that's not initialised at that stage.  See the call to
setup_per_cpu_areas() a few lines later.

So I'll drop that hunk.  How important is it in practice?

If it's purely to make printk print something then perhaps we can do
something expedient like:

#ifdef CONFIG_SMP
	cpu_set(smp_processor_id(), cpu_online_map);	/* comment */
#endif

right there in start_kernel()?

(That assumes that smp_processor_id() works at that stage.  Surely that's
true).