From 29b4eedee67b449534214058e1bcb36307a7f1dc Mon Sep 17 00:00:00 2001 From: Wanpeng Li Date: Wed, 11 Sep 2013 14:22:59 -0700 Subject: [PATCH] mm/hwpoison.c: fix held reference count after unpoisoning empty zero page madvise hwpoison inject will poison the read-only empty zero page if there is no write access before poison. Empty zero page reference count will be increased for hwpoison, subsequent poison zero page will return directly since page has already been set PG_hwpoison, however, page reference count is still increased by get_user_pages_fast. The unpoison process will unpoison the empty zero page and decrease the reference count successfully for the fist time, however, subsequent unpoison empty zero page will return directly since page has already been unpoisoned and without decrease the page reference count of empty zero page. This patch fixes it by make madvise_hwpoison() put a page and return immediately (without calling memory_failure() or soft_offline_page()) when the page is already hwpoisoned. Testcase: #define _GNU_SOURCE #include #include #include #include #include #include #include #define PAGES_TO_TEST 3 #define PAGE_SIZE 4096 int main(void) { char *mem; int i; mem = mmap(NULL, PAGES_TO_TEST * PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); if (madvise(mem, PAGES_TO_TEST * PAGE_SIZE, MADV_HWPOISON) == -1) return -1; munmap(mem, PAGES_TO_TEST * PAGE_SIZE); return 0; } Add printk to dump page reference count: [ 93.075959] Injecting memory failure for page 0x19d0 at 0xb77d8000 [ 93.076207] MCE 0x19d0: non LRU page recovery: Ignored [ 93.076209] pfn 0x19d0, page count = 1 after memory failure [ 93.076220] Injecting memory failure for page 0x19d0 at 0xb77d9000 [ 93.076221] MCE 0x19d0: already hardware poisoned [ 93.076222] pfn 0x19d0, page count = 2 after memory failure [ 93.076224] Injecting memory failure for page 0x19d0 at 0xb77da000 [ 93.076224] MCE 0x19d0: already hardware poisoned [ 93.076225] pfn 0x19d0, page count = 3 after memory failure Signed-off-by: Wanpeng Li Suggested-by: Naoya Horiguchi Cc: Andi Kleen Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/madvise.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/madvise.c b/mm/madvise.c index 9b1c7be182d7..30293ab95b06 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -352,6 +352,10 @@ static int madvise_hwpoison(int bhv, unsigned long start, unsigned long end) int ret = get_user_pages_fast(start, 1, 0, &p); if (ret != 1) return ret; + if (PageHWPoison(p)) { + put_page(p); + continue; + } if (bhv == MADV_SOFT_OFFLINE) { pr_info("Soft offlining page %#lx at %#lx\n", page_to_pfn(p), start); -- 2.39.5