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=-8.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 8215FC07E99 for ; Mon, 5 Jul 2021 16:09:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6640E61968 for ; Mon, 5 Jul 2021 16:09:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229740AbhGEQL7 (ORCPT ); Mon, 5 Jul 2021 12:11:59 -0400 Received: from mail.kernel.org ([198.145.29.99]:49554 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229495AbhGEQL6 (ORCPT ); Mon, 5 Jul 2021 12:11:58 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 62D73613AB; Mon, 5 Jul 2021 16:09:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1625501361; bh=2XzMBDCWTuZKTJpPDkKpokzuPVPOTBI/2bclffIorx4=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=u7D924a+RJH1J56edLLyj9U6oNbUsWpUHVDhsrgfQpJGWcXCcn7WbgahQeBWXD1bz PCrSCeCTpGQkJZo3ZkfMiDVRRhV+nIhnT2wC1wo/IfLfyfRPV9VOBo9TIoH3Xm9URD QXGL2qKbavinIC1Iik8uGys28/D8IEroD2tuTox4ZPCAPA32skpiohwQJgzXidUYAW ryZr0JjzJHbzibg4KUyv8t/U9wtjtKwhY2RhJD3ACP5Fa3NHiIKtX2cQp0IqOYk/CF momhsPDmeAgGI8YuLyeiHrsvpInbnw7lFVfCxk6tifSHxpSEc9ELsJykzl72cCpWba xYTjLdDVji5Gw== Subject: Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for our internal use To: Matthew Wilcox , Jaegeuk Kim Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-mm@kvack.org References: <20210705052216.831989-1-jaegeuk@kernel.org> From: Chao Yu Message-ID: <5ab8d01a-8fac-60b2-9c2c-a32c5a81b394@kernel.org> Date: Tue, 6 Jul 2021 00:09:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/7/5 19:47, Matthew Wilcox wrote: > On Mon, Jul 05, 2021 at 07:33:35PM +0800, Chao Yu wrote: >> On 2021/7/5 16:56, Jaegeuk Kim wrote: >>> On 07/05, Chao Yu wrote: >>>> On 2021/7/5 13:22, Jaegeuk Kim wrote: >>>>> We need to guarantee it's initially zero. Otherwise, it'll hurt entire flag >>>>> operations. >>>> >>>> Oops, I didn't get the point, shouldn't .private be zero after page was >>>> just allocated by filesystem? What's the case we will encounter stall >>>> private data left in page? >>> >>> I'm seeing f2fs_migrate_page() has the newpage with some value without Private >>> flag. That causes a kernel panic later due to wrong private flag used in f2fs. >> >> I'm not familiar with that part of codes, so Cc mm mailing list for help. >> >> My question is newpage in .migrate_page() may contain non-zero value in .private >> field but w/o setting PagePrivate flag, is it a normal case? > > I think freshly allocated pages have a page->private of 0. ie this > code in mm/page_alloc.c: > > page = rmqueue(ac->preferred_zoneref->zone, zone, order, > gfp_mask, alloc_flags, ac->migratetype); > if (page) { > prep_new_page(page, order, gfp_mask, alloc_flags); > > where prep_new_page() calls post_alloc_hook() which contains: > set_page_private(page, 0); > > Now, I do see in __buffer_migrate_page() (mm/migrate.c): > > attach_page_private(newpage, detach_page_private(page)); > > but as far as I can tell, f2fs doesn't call any of the > buffer_migrate_page() paths. So I'm not sure why you're seeing > a non-zero page->private. Well, that's strange. Jaegeuk, let's add a BUGON in f2fs to track the call path where newpage has non-zero private value? if this issue is reproducible. Thanks, >