From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx189.postini.com [74.125.245.189]) by kanga.kvack.org (Postfix) with SMTP id 6488E6B0033 for ; Mon, 26 Aug 2013 19:26:18 -0400 (EDT) Received: from /spool/local by e28smtp02.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 27 Aug 2013 04:45:53 +0530 Received: from d28relay03.in.ibm.com (d28relay03.in.ibm.com [9.184.220.60]) by d28dlp02.in.ibm.com (Postfix) with ESMTP id B387C3940058 for ; Tue, 27 Aug 2013 04:55:56 +0530 (IST) Received: from d28av01.in.ibm.com (d28av01.in.ibm.com [9.184.220.63]) by d28relay03.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r7QNRgsT19267676 for ; Tue, 27 Aug 2013 04:57:43 +0530 Received: from d28av01.in.ibm.com (localhost [127.0.0.1]) by d28av01.in.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id r7QNQ5rl003186 for ; Tue, 27 Aug 2013 04:56:06 +0530 Date: Tue, 27 Aug 2013 07:26:04 +0800 From: Wanpeng Li Subject: Re: [PATCH v4 8/10] mm/hwpoison: fix memory failure still hold reference count after unpoison empty zero page Message-ID: <20130826232604.GA12498@hacker.(null)> Reply-To: Wanpeng Li References: <1377506774-5377-1-git-send-email-liwanp@linux.vnet.ibm.com> <1377506774-5377-8-git-send-email-liwanp@linux.vnet.ibm.com> <1377531937-15nx3q8e-mutt-n-horiguchi@ah.jp.nec.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377531937-15nx3q8e-mutt-n-horiguchi@ah.jp.nec.com> Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Andrew Morton , Andi Kleen , Fengguang Wu , Tony Luck , gong.chen@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Naoya, On Mon, Aug 26, 2013 at 11:45:37AM -0400, Naoya Horiguchi wrote: >On Mon, Aug 26, 2013 at 04:46:12PM +0800, Wanpeng Li wrote: >> 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 fix it by decrease page reference count for empty zero page which has >> already been unpoisoned and page count > 1. > >I guess that fixing on the madvise side looks reasonable to me, because this >refcount mismatch happens only when we poison with madvise(). The root cause >is that we can get refcount multiple times on a page, even if memory_failure() >or soft_offline_page() can do its work only once. > I think this just happen in read-only before poison case against empty zero page. Hi Andrew, I see you have already merged the patch, which method you prefer? >How about making madvise_hwpoison() put a page and return immediately >(without calling memory_failure() or soft_offline_page()) when the page >is already hwpoisoned? >I hope it also helps us avoid meaningless printk flood. > Btw, Naoya, how about patch 10/10, any input are welcome! ;-) Regards, Wanpeng Li >Thanks, >Naoya Horiguchi > >> 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 >> >> Before patch: >> >> [ 139.197474] MCE: Software-unpoisoned page 0x19d0 >> [ 139.197479] pfn 0x19d0, page count = 2 after unpoison memory >> [ 150.478130] MCE: Page was already unpoisoned 0x19d0 >> [ 150.478135] pfn 0x19d0, page count = 2 after unpoison memory >> [ 151.548288] MCE: Page was already unpoisoned 0x19d0 >> [ 151.548292] pfn 0x19d0, page count = 2 after unpoison memory >> >> After patch: >> >> [ 116.022122] MCE: Software-unpoisoned page 0x19d0 >> [ 116.022127] pfn 0x19d0, page count = 2 after unpoison memory >> [ 117.256163] MCE: Page was already unpoisoned 0x19d0 >> [ 117.256167] pfn 0x19d0, page count = 1 after unpoison memory >> [ 117.917772] MCE: Page was already unpoisoned 0x19d0 >> [ 117.917777] pfn 0x19d0, page count = 1 after unpoison memory >> >> Signed-off-by: Wanpeng Li >> --- >> mm/memory-failure.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index ca714ac..fb687fd 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1335,6 +1335,8 @@ int unpoison_memory(unsigned long pfn) >> page = compound_head(p); >> >> if (!PageHWPoison(p)) { >> + if (pfn == my_zero_pfn(0) && page_count(p) > 1) >> + put_page(p); >> pr_info("MCE: Page was already unpoisoned %#lx\n", pfn); >> return 0; >> } >> -- >> 1.8.1.2 >> > >-- >To unsubscribe, send a message with 'unsubscribe linux-mm' in >the body to majordomo@kvack.org. For more info on Linux MM, >see: http://www.linux-mm.org/ . >Don't email: email@kvack.org -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org