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=-17.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 E5A74C433FE for ; Mon, 6 Sep 2021 12:45:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6D3286108E for ; Mon, 6 Sep 2021 12:45:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6D3286108E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id BD8096B0071; Mon, 6 Sep 2021 08:45:19 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B876A6B0072; Mon, 6 Sep 2021 08:45:19 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A50256B0073; Mon, 6 Sep 2021 08:45:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0094.hostedemail.com [216.40.44.94]) by kanga.kvack.org (Postfix) with ESMTP id 9559D6B0071 for ; Mon, 6 Sep 2021 08:45:19 -0400 (EDT) Received: from smtpin40.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 465168249980 for ; Mon, 6 Sep 2021 12:45:19 +0000 (UTC) X-FDA: 78557119158.40.FA39D80 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by imf07.hostedemail.com (Postfix) with ESMTP id 1C6DA10000B9 for ; Mon, 6 Sep 2021 12:45:17 +0000 (UTC) Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4H37LL6hX4zbkXS; Mon, 6 Sep 2021 20:41:14 +0800 (CST) Received: from [10.174.178.100] (10.174.178.100) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Mon, 6 Sep 2021 20:45:13 +0800 Subject: Re: [PATCH] mm/page_isolation: don't putback unisolated page To: David Hildenbrand , CC: , , , References: <20210904091839.20270-1-linmiaohe@huawei.com> <3b36529f-ab97-ddfe-0407-66f0cd1fd38d@redhat.com> <2d06db75-5c26-8fe2-6883-ac99056a9894@redhat.com> From: Miaohe Lin Message-ID: Date: Mon, 6 Sep 2021 20:45:13 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <2d06db75-5c26-8fe2-6883-ac99056a9894@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US X-Originating-IP: [10.174.178.100] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Authentication-Results: imf07.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=huawei.com; spf=pass (imf07.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.187 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: 84bp8zww5f5ssean6d9q4k5g1rc76xk1 X-Rspamd-Queue-Id: 1C6DA10000B9 X-Rspamd-Server: rspam04 X-HE-Tag: 1630932317-727344 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2021/9/6 20:11, David Hildenbrand wrote: > On 06.09.21 14:02, David Hildenbrand wrote: >> On 04.09.21 11:18, Miaohe Lin wrote: >>> If __isolate_free_page() failed, due to zone watermark check, the pag= e is >>> still on the free list. But this page will be put back to free list a= gain >>> via __putback_isolated_page() now. This may trigger page->flags check= s in >>> __free_one_page() if PageReported is set. Or we will corrupt the free= list >>> because list_add() will be called for pages already on another list. >>> >>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on= isolated pageblock") >>> Signed-off-by: Miaohe Lin >>> --- >>> =C2=A0=C2=A0 mm/page_isolation.c | 6 ++---- >>> =C2=A0=C2=A0 1 file changed, 2 insertions(+), 4 deletions(-) >>> >>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c >>> index 9bb562d5d194..7d70d772525c 100644 >>> --- a/mm/page_isolation.c >>> +++ b/mm/page_isolation.c >>> @@ -93,10 +93,8 @@ static void unset_migratetype_isolate(struct page = *page, unsigned migratetype) >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 buddy_pfn =3D __find_buddy_pfn(pfn, order); >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 buddy =3D page + (buddy_pfn - pfn); >>> =C2=A0=C2=A0 -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 if (!is_migrate_isolate_page(buddy)) { >>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 __isolate_free_page(page, order); >>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 isolated_page =3D true; >>> -=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i= f (!is_migrate_isolate_page(buddy)) >>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 isolated_page =3D !!__isolate_free_page(page, order= ); >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 } >>> =C2=A0=C2=A0 >> >> Thanks! >> >> Reviewed-by: David Hildenbrand >> >=20 > To make the confusion perfect (sorry) :D I tripple-checked: >=20 > In unset_migratetype_isolate() we check that is_migrate_isolate_page(pa= ge) holds, otherwise we return. >=20 > We call __isolate_free_page() only for such pages. >=20 > __isolate_free_page() won't perform watermark checks on is_migrate_isol= ate(). >=20 > Consequently, __isolate_free_page() should never fail when called from = unset_migratetype_isolate() >=20 > If that's correct then we=C2=A0 could instead maybe add a VM_BUG_ON() a= nd a comment why this can't fail. >=20 >=20 > Makes sense or am I missing something? I think you're right. __isolate_free_page() should never fail when called= from unset_migratetype_isolate() as explained by you. But it might be too fragile to reply on the failure = conditions of __isolate_free_page(). If that changes, VM_BUG_ON() here might trigger unexpectedly. Or am I jus= t over-worried as failure conditions of __isolate_free_page() can hardly change? Many thanks. :) >=20