debug-pagealloc.c

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#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/page-debug-flags.h>
#include <linux/poison.h>
#include <linux/ratelimit.h>

static inline void set_page_poison(struct page *page)
{
    __set_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
}

static inline void clear_page_poison(struct page *page)
{
    __clear_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
}

static inline bool page_poison(struct page *page)
{
    return test_bit(PAGE_DEBUG_FLAG_POISON, &page->debug_flags);
}

static void poison_page(struct page *page)
{
    void *addr = kmap_atomic(page);

    set_page_poison(page);
    memset(addr, PAGE_POISON, PAGE_SIZE);
    kunmap_atomic(addr);
}

static void poison_pages(struct page *page, int n)
{
    int i;

    for (i = 0; i < n; i++)
        poison_page(page + i);
}

static bool single_bit_flip(unsigned char a, unsigned char b)
{
    unsigned char error = a ^ b;

    return error && !(error & (error - 1));
}

static void check_poison_mem(unsigned char *mem, size_t bytes)
{
    static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
    unsigned char *start;
    unsigned char *end;

    start = memchr_inv(mem, PAGE_POISON, bytes);
    if (!start)
        return;

    for (end = mem + bytes - 1; end > start; end--) {
        if (*end != PAGE_POISON)
            break;
    }

    if (!__ratelimit(&ratelimit))
        return;
    else if (start == end && single_bit_flip(*start, PAGE_POISON))
        printk(KERN_ERR "pagealloc: single bit error\n");
    else
        printk(KERN_ERR "pagealloc: memory corruption\n");

    print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
            end - start + 1, 1);
    dump_stack();
}

static void unpoison_page(struct page *page)
{
    void *addr;

    if (!page_poison(page))
        return;

    addr = kmap_atomic(page);
    check_poison_mem(addr, PAGE_SIZE);
    clear_page_poison(page);
    kunmap_atomic(addr);
}

static void unpoison_pages(struct page *page, int n)
{
    int i;

    for (i = 0; i < n; i++)
        unpoison_page(page + i);
}

void kernel_map_pages(struct page *page, int numpages, int enable)
{
    if (enable)
        unpoison_pages(page, numpages);
    else
        poison_pages(page, numpages);
}