From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx129.postini.com [74.125.245.129]) by kanga.kvack.org (Postfix) with SMTP id A56046B0062 for ; Mon, 10 Dec 2012 03:33:54 -0500 (EST) Received: from /spool/local by e23smtp02.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 10 Dec 2012 18:29:46 +1000 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [9.190.234.120]) by d23dlp03.au.ibm.com (Postfix) with ESMTP id 2C1033578023 for ; Mon, 10 Dec 2012 19:33:46 +1100 (EST) Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id qBA8Mp3i66977914 for ; Mon, 10 Dec 2012 19:22:52 +1100 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id qBA8XiAm026318 for ; Mon, 10 Dec 2012 19:33:45 +1100 Date: Mon, 10 Dec 2012 16:33:42 +0800 From: Wanpeng Li Subject: Re: [PATCH V2] MCE: fix an error of mce_bad_pages statistics Message-ID: <20121210083342.GA31670@hacker.(null)> Reply-To: Wanpeng Li References: <50C1AD6D.7010709@huawei.com> <20121207141102.4fda582d.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121207141102.4fda582d.akpm@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Xishi Qiu Cc: WuJianguo , Liujiang , Vyacheslav.Dubeyko@huawei.com, Borislav Petkov , andi@firstfloor.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, Dec 07, 2012 at 02:11:02PM -0800, Andrew Morton wrote: >On Fri, 7 Dec 2012 16:48:45 +0800 >Xishi Qiu wrote: > >> On x86 platform, if we use "/sys/devices/system/memory/soft_offline_page" to offline a >> free page twice, the value of mce_bad_pages will be added twice. So this is an error, >> since the page was already marked HWPoison, we should skip the page and don't add the >> value of mce_bad_pages. >> >> $ cat /proc/meminfo | grep HardwareCorrupted >> >> soft_offline_page() >> get_any_page() >> atomic_long_add(1, &mce_bad_pages) >> >> ... >> >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1582,8 +1582,11 @@ int soft_offline_page(struct page *page, int flags) >> return ret; >> >> done: >> - atomic_long_add(1, &mce_bad_pages); >> - SetPageHWPoison(page); >> /* keep elevated page count for bad page */ >> + if (!PageHWPoison(page)) { >> + atomic_long_add(1, &mce_bad_pages); >> + SetPageHWPoison(page); >> + } >> + >> return ret; >> } > >A few things: > >- soft_offline_page() already checks for this case: > > if (PageHWPoison(page)) { > unlock_page(page); > put_page(page); > pr_info("soft offline: %#lx page already poisoned\n", pfn); > return -EBUSY; > } > > so why didn't this check work for you? > > Presumably because one of the earlier "goto done" branches was > taken. Which one, any why? > > This function is an utter mess. It contains six return points > randomly intermingled with three "goto done" return points. > > This mess is probably the cause of the bug you have observed. Can > we please fix it up somehow? It *seems* that the design (lol) of > this function is "for errors, return immediately. For success, goto > done". In which case "done" should have been called "success". But > if you just look at the function you'll see that this approach didn't > work. I suggest it be converted to have two return points - one for > the success path, one for the failure path. Or something. > >- soft_offline_huge_page() is a miniature copy of soft_offline_page() > and might suffer the same bug. > >- A cleaner, shorter and possibly faster implementation is > > if (!TestSetPageHWPoison(page)) > atomic_long_add(1, &mce_bad_pages); > Hi Andrew, Since hwpoison bit for free buddy page has already be set in get_any_page, !TestSetPageHWPoison(page) will not increase mce_bad_pages count even for the first time. Regards, Wanpeng Li >- We have atomic_long_inc(). Use it? > >- Why do we have a variable called "mce_bad_pages"? MCE is an x86 > concept, and this code is in mm/. Lights are flashing, bells are > ringing and a loudspeaker is blaring "layering violation" at us! > >-- >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