From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ECBF0C433ED for ; Mon, 17 May 2021 06:48:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CEE3361185 for ; Mon, 17 May 2021 06:48:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233732AbhEQGuF (ORCPT ); Mon, 17 May 2021 02:50:05 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:3707 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229628AbhEQGuF (ORCPT ); Mon, 17 May 2021 02:50:05 -0400 Received: from dggems705-chm.china.huawei.com (unknown [172.30.72.58]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4Fk8mC5c9Kz16QxW; Mon, 17 May 2021 14:46:03 +0800 (CST) Received: from dggema766-chm.china.huawei.com (10.1.198.208) by dggems705-chm.china.huawei.com (10.3.19.182) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Mon, 17 May 2021 14:48:47 +0800 Received: from [10.174.177.210] (10.174.177.210) by dggema766-chm.china.huawei.com (10.1.198.208) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Mon, 17 May 2021 14:48:47 +0800 Subject: Re: [PATCH] mm/memory-failure: make sure wait for page writeback in memory_failure To: Oscar Salvador , Jan Kara , CC: , , , , , , , , , References: <20210511070329.2002597-1-yangerkun@huawei.com> <20210511084600.GG24154@quack2.suse.cz> From: yangerkun Message-ID: <4803a723-666f-c710-3ad4-2579390e4a9d@huawei.com> Date: Mon, 17 May 2021 14:48:46 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.210] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggema766-chm.china.huawei.com (10.1.198.208) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 在 2021/5/11 17:34, Oscar Salvador 写道: > On Tue, May 11, 2021 at 10:46:00AM +0200, Jan Kara wrote: >> We definitely need to wait for writeback of these pages and the change you >> suggest makes sense to me. I'm just not sure whether the only problem with >> these "pages in the process of being munlocked()" cannot confuse the state >> machinery in memory_failure() also in some other way. Also I'm not sure if >> are really allowed to call wait_on_page_writeback() on just any page that >> hits memory_failure() - there can be slab pages, anon pages, completely >> unknown pages given out by page allocator to device drivers etc. That needs >> someone more familiar with these MM details than me. > > I am not really into mm/writeback stuff, but: > > shake_page() a few lines before tries to identifiy the page, and > make those sitting in lruvec real PageLRU, and then we take page's lock. > > I thought that such pages (pages on writeback) are stored in the file > LRU, and maybe the code was written with that in mind? And given that > we are under the PageLock, such state could not have changed. Hi, Crash of this bug show we can clear page LRU without lock_page by follow stack. So this page_lock in memory_failure seems useless to prevent this BUG. do_mmap->mmap_region->do_munmap->munlock_vma_pages_range->__munlock_pagevec static void __munlock_pagevec(struct pagevec *pvec, struct zone *zone) { ... for (i = 0; i < nr; i++) { struct page *page = pvec->pages[i]; if (TestClearPageMlocked(page)) { if (TestClearPageLRU(page)) { <=== clear LRU flag ... } ... } ... } ... } > > But if such pages are allowed to not be in the LRU (maybe they are taken > off before initiating the writeback?), I guess the change is correct. > Checking wait_on_page_writeback(), it seems it first checks for > Writeback bit, and since that bit is not "shared" and only being set > in mm/writeback code, it should be fine to call that. > > But alternatively, we could also modify the check and go with: > > if (!PageTransTail(p) && !PageLRU(p) && !PageWriteBack(p)) > goto identify_page_state; I have no idea should we process this page with such state. But it seems reasonable to add some comments to clarify our change. Thanks, Kun. > > and stating why a page under writeback might not be in the LRU, as I > think the code assumes. > > AFAUI, mm/writeback locks the page before setting the bit, and since we > hold the lock, we could not race here. >