From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx182.postini.com [74.125.245.182]) by kanga.kvack.org (Postfix) with SMTP id 52ECF6B005A for ; Sun, 9 Dec 2012 23:39:53 -0500 (EST) Message-ID: <50C5660D.4050805@huawei.com> Date: Mon, 10 Dec 2012 12:33:17 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [PATCH V2] MCE: fix an error of mce_bad_pages statistics References: <50C1AD6D.7010709@huawei.com> <20121207141102.4fda582d.akpm@linux-foundation.org> In-Reply-To: <20121207141102.4fda582d.akpm@linux-foundation.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: WuJianguo , Liujiang , Vyacheslav.Dubeyko@huawei.com, Borislav Petkov , andi@firstfloor.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On 2012/12/8 6:11, 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); > > - 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! > Hi Andrew, thank you for your advice, I will send V3 soon. Thanks Xishi Qiu > . > -- 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