Re: [PATCH] powerpc: mem_init crash for sparsemem

[Andy Whitcroft <apw@shadowen.org>]

Arnd Bergmann wrote:
> I have a Cell blade with some broken memory in the middle of the
> physical address space and this is correctly detected by the
> firmware, but not relocated. When I enable CONFIG_SPARSEMEM,
> the memsections for the nonexistant address space do not
> get struct page entries allocated, as expected.
> 
> However, mem_init for the non-NUMA configuration tries to
> access these pages without first looking if they are there.
> I'm currently using the hack below to work around that, but
> I have the feeling that there should be a cleaner solution
> for this.
> 
> Please comment.
> 
> Signed-off-by: Arnd Bergmann <arndb@de.ibm.com>
> 
> --- linux-2.6.15-rc.orig/arch/powerpc/mm/mem.c
> +++ linux-2.6.15-rc/arch/powerpc/mm/mem.c
> @@ -348,6 +348,9 @@ void __init mem_init(void)
>  #endif
>  	for_each_pgdat(pgdat) {
>  		for (i = 0; i < pgdat->node_spanned_pages; i++) {
> +			if (!section_has_mem_map(__pfn_to_section
> +					(pgdat->node_start_pfn + i)))
> +				continue;
>  			page = pgdat_page_nr(pgdat, i);
>  			if (PageReserved(page))
>  				reservedpages++;

Would it not make sense to use pfn_valid(), as that is not sparsemem
specific?  Not looked at the code in question specifically, but if you
can use section_has_mem_map() it should be equivalent:

	if (!pfn_valid(pgdat->node_start_pfn + i))
		continue;

Want to spin us a patch and I'll give it some general testing.

-apw