Re: [PATCH] generic debug pagealloc (-v2)

Andrew Morton
2009-03-05T22:32:51Z

On Thu, 5 Mar 2009 23:59:27 +0900
Akinobu Mita <akinobu.mita@gmail.com> wrote:

> CONFIG_DEBUG_PAGEALLOC is now supported by x86, powerpc, sparc (64bit),
> and s390. This patch implements it for the rest of the architectures
> by filling the pages with poison byte patterns after free_pages() and
> verifying the poison patterns before alloc_pages().
>
> This generic one cannot detect invalid read accesses and it can only
> detect invalid write accesses after a long delay. But it is a feasible way
> for nommu architectures.
>
> ...
>
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +
> +static void poison_page(struct page *page)
> +{
> + void *addr;
> +
> + if (PageHighMem(page))
> + return; /* i goofed */

heh. A more complete comment would be needed here.

Also, as this is a kernel bug, perhaps some sort of runtime warning?

> + page->poison = true;
> + addr = page_address(page);
> + memset(addr, PAGE_POISON, PAGE_SIZE);
> +}
> +
> +static void poison_pages(struct page *page, int n)
> +{
> + int i;
> +
> + for (i = 0; i < n; i++)
> + poison_page(page + i);
> +}
> +
> +static void check_poison_mem(unsigned char *mem, size_t bytes)
> +{
> + unsigned char *start;
> + unsigned char *end;
> +
> + for (start = mem; start < mem + bytes; start++) {
> + if (*start != PAGE_POISON)
> + break;
> + }
> + if (start == mem + bytes)
> + return;
> +
> + for (end = mem + bytes - 1; end > start; end--) {
> + if (*end != PAGE_POISON)
> + break;
> + }
> + printk(KERN_ERR "Page corruption: %p-%p\n", start, end);
> + print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
> + end - start + 1, 1);
> +}
> +
> +static void unpoison_page(struct page *page)
> +{
> + void *addr;
> +

Shouldn't we check PageHighmem() here also?

> + if (!page->poison)
> + return;
> +
> + addr = page_address(page);
> + check_poison_mem(addr, PAGE_SIZE);
> + page->poison = false;
> +}
> +