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=-15.3 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=unavailable 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 8B48CC433B4 for ; Mon, 10 May 2021 06:57:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 019BE61432 for ; Mon, 10 May 2021 06:57:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 019BE61432 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 17B376B0070; Mon, 10 May 2021 02:57:18 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 12B3B6B0071; Mon, 10 May 2021 02:57:18 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 019F96B0072; Mon, 10 May 2021 02:57:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0132.hostedemail.com [216.40.44.132]) by kanga.kvack.org (Postfix) with ESMTP id D7C2C6B0070 for ; Mon, 10 May 2021 02:57:17 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 84D9A8249980 for ; Mon, 10 May 2021 06:57:17 +0000 (UTC) X-FDA: 78124414914.18.B0D09EC Received: from szxga07-in.huawei.com (szxga07-in.huawei.com [45.249.212.35]) by imf29.hostedemail.com (Postfix) with ESMTP id 7B0C5135 for ; Mon, 10 May 2021 06:57:10 +0000 (UTC) Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.59]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4FdsHC2SwVzCqrG; Mon, 10 May 2021 14:54:31 +0800 (CST) Received: from [10.174.176.232] (10.174.176.232) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.498.0; Mon, 10 May 2021 14:57:06 +0800 Subject: Re: [PATCH] ksm: Revert "use GET_KSM_PAGE_NOLOCK to get ksm page in remove_rmap_item_from_tree()" To: Hugh Dickins , Andrew Morton CC: , References: From: Miaohe Lin Message-ID: <0e04877c-5b2d-b810-7464-108e793b84d3@huawei.com> Date: Mon, 10 May 2021 14:57:06 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.232] X-CFilter-Loop: Reflected Authentication-Results: imf29.hostedemail.com; dkim=none; spf=pass (imf29.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.35 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-Stat-Signature: 6refnfhmicsa8d617naieufx4wup5z9z X-Rspamd-Queue-Id: 7B0C5135 X-Rspamd-Server: rspam05 Received-SPF: none (huawei.com>: No applicable sender policy available) receiver=imf29; identity=mailfrom; envelope-from=""; helo=szxga07-in.huawei.com; client-ip=45.249.212.35 X-HE-DKIM-Result: none/none X-HE-Tag: 1620629830-703855 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 2021/5/10 13:59, Hugh Dickins wrote: > This reverts commit 3e96b6a2e9ad929a3230a22f4d64a74671a0720b. > General Protection Fault in rmap_walk_ksm() under memory pressure: > remove_rmap_item_from_tree() needs to take page lock, of course. > I'am really sorry about it! And many thanks for this bugfix! It seems rmap_walk_ksm() relies on the page lock to protect against concurrent modifications to that page's node of the stable tree. Could you please add a comment in remove_rmap_item_from_tree() to clarify this in case similar trouble again? Many thanks! > Signed-off-by: Hugh Dickins > --- > > mm/ksm.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > --- 5.13-rc1/mm/ksm.c 2021-05-09 17:03:44.010422188 -0700 > +++ linux/mm/ksm.c 2021-05-09 22:12:39.403008350 -0700 > @@ -776,11 +776,12 @@ static void remove_rmap_item_from_tree(s > struct page *page; > > stable_node = rmap_item->head; > - page = get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK); > + page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK); > if (!page) > goto out; > > hlist_del(&rmap_item->hlist); > + unlock_page(page); > put_page(page); > > if (!hlist_empty(&stable_node->hlist)) > . >