On Wed, 2011-06-08 at 15:18 -0400, Eric B Munson wrote:
> -#define __pfn_to_page(pfn) \
> -({ unsigned long __pfn = (pfn); \
> - struct mem_section *__sec = __pfn_to_section(__pfn); \
> - __section_mem_map_addr(__sec) + __pfn; \
> +#ifdef CONFIG_DEBUG_MEMORY_MODEL
> +#define __pfn_to_page(pfn) \
> +({ unsigned long __pfn = (pfn); \
> + struct mem_section *__sec = __pfn_to_section(__pfn); \
> + struct page *__page = __section_mem_map_addr(__sec) + __pfn; \
> + WARN_ON(__page->flags == 0); \
> + __page; \
What was the scenario you're trying to catch here? If you give a really
crummy __pfn, you'll probably go off the end of one of the mem_section[]
arrays, and get garbage back for __sec. You might also get a NULL back
from __section_mem_map_addr() if the section is possibly valid, but just
not present on this particular system.
I _think_ the only kind of bug this will catch is if you have a valid
section, with a valid section_mem_map[] but still manage to find
yourself with an 'struct page' unclaimed by any zone and thus
uninitialized.
You could catch a lot more cases by being a bit more paranoid:
void check_pfn(unsigned long pfn)
{
int nid;
// hacked in from pfn_to_nid:
// Don't actually do this, add a new helper near pfn_to_nid()
// Can this even fit in the physnode_map?
if (pfn / PAGES_PER_ELEMENT > ARRAY_SIZE(physnode_map))
WARN();
// Is there a valid nid there?
nid = pfn_to_nid(pfn);
if (nid == -1)
WARN();
// check against NODE_DATA(nid)->node_start_pfn;
// check against NODE_DATA(nid)->node_spanned_pages;
}
> })
> +#else
> +#define __pfn_to_page(pfn) \
> +({ unsigned long __pfn = (pfn); \
> + struct mem_section *__sec = __pfn_to_section(__pfn); \
> + __section_mem_map_addr(__sec) + __pfn; \
> +})
> +#endif /* CONFIG_DEBUG_MEMORY_MODEL */
Instead of making a completely new __pfn_to_page() in the debugging
case, I'd probably do something like this:
#ifdef CONFIG_DEBUG_MEMORY_MODEL
#define check_foo(foo) {\
some_check_here(foo);\
WARN_ON(foo->flags);\
}
#else
#define check_foo(foo) do{}while(0)
#endif;
#define __pfn_to_page(pfn) \
({ unsigned long __pfn = (pfn); \
struct mem_section *__sec = __pfn_to_section(__pfn); \
struct page *__page = __section_mem_map_addr(__sec) + __pfn; \
check_foo(page) \
__page; \
})
That'll make sure that the two copies of __pfn_to_page() don't
accidentally diverge. It also makes it a lot easier to read, I think.
-- Dave
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