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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3EC61EB64DA for ; Sat, 8 Jul 2023 09:00:33 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4QykkS1wcGz3bvX for ; Sat, 8 Jul 2023 19:00:32 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.alibaba.com (client-ip=115.124.30.112; helo=out30-112.freemail.mail.aliyun.com; envelope-from=hsiangkao@linux.alibaba.com; receiver=lists.ozlabs.org) Received: from out30-112.freemail.mail.aliyun.com (out30-112.freemail.mail.aliyun.com [115.124.30.112]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4QykkH36gwz2xqp for ; Sat, 8 Jul 2023 19:00:21 +1000 (AEST) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R711e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018046050;MF=hsiangkao@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0VmrW6mA_1688806814; Received: from 172.20.10.3(mailfrom:hsiangkao@linux.alibaba.com fp:SMTPD_---0VmrW6mA_1688806814) by smtp.aliyun-inc.com; Sat, 08 Jul 2023 17:00:16 +0800 Message-ID: <97875049-8df9-e041-61ca-d90723ba6e82@linux.alibaba.com> Date: Sat, 8 Jul 2023 17:00:09 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] erofs: fix two loop issues when read page beyond EOF To: Chunhai Guo , xiang@kernel.org, chao@kernel.org References: <20230708062432.67344-1-guochunhai@vivo.com> From: Gao Xiang In-Reply-To: <20230708062432.67344-1-guochunhai@vivo.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: linux-erofs@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Development of Linux EROFS file system List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: huyue2@coolpad.com, linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linux-erofs-bounces+linux-erofs=archiver.kernel.org@lists.ozlabs.org Sender: "Linux-erofs" Hi Chunhai, On 2023/7/8 14:24, Chunhai Guo wrote: > When z_erofs_read_folio() reads a page with an offset far beyond EOF, two > issues may occur: > - z_erofs_pcluster_readmore() may take a long time to loop when the offset > is big enough, which is unnecessary. > - For example, it will loop 4691368 times and take about 27 seconds > with following case. > - offset = 19217289215 > - inode_size = 1442672 > - z_erofs_do_read_page() may loop infinitely due to the inappropriate > truncation in the below statement. Since the offset is 64 bits and > min_t() truncates the result to 32 bits. The solution is to replace > unsigned int with another 64-bit type, such as erofs_off_t. > cur = end - min_t(unsigned int, offset + end - map->m_la, end); > - For example: > - offset = 0x400160000 > - end = 0x370 > - map->m_la = 0x160370 > - offset + end - map->m_la = 0x400000000 > - offset + end - map->m_la = 0x00000000 (truncated as unsigned int) Thanks for the catch! Could you split these two into two patches? how about using: cur = end - min_t(erofs_off_t, offend + end - map->m_la, end) for this? since cur and end are all [0, PAGE_SIZE - 1] for now, and folio_size() later. > - Expected result: > - cur = 0 > - Actual result: > - cur = 0x370 > > Signed-off-by: Chunhai Guo > --- > fs/erofs/zdata.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c > index 5f1890e309c6..6abbd4510076 100644 > --- a/fs/erofs/zdata.c > +++ b/fs/erofs/zdata.c > @@ -972,7 +972,8 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, > struct erofs_map_blocks *const map = &fe->map; > const loff_t offset = page_offset(page); > bool tight = true, exclusive; > - unsigned int cur, end, spiltted; > + erofs_off_t cur, end; > + unsigned int spiltted; > int err = 0; > > /* register locked file pages as online pages in pack */ > @@ -1035,7 +1036,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe, > */ > tight &= (fe->mode > Z_EROFS_PCLUSTER_FOLLOWED_NOINPLACE); > > - cur = end - min_t(unsigned int, offset + end - map->m_la, end); > + cur = end - min_t(erofs_off_t, offset + end - map->m_la, end); > if (!(map->m_flags & EROFS_MAP_MAPPED)) { > zero_user_segment(page, cur, end); > goto next_part; > @@ -1841,7 +1842,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f, > } > > cur = map->m_la + map->m_llen - 1; > - while (cur >= end) { > + while ((cur >= end) && (cur < i_size_read(inode))) { > pgoff_t index = cur >> PAGE_SHIFT; > struct page *page; > > @@ -1876,6 +1877,12 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio) > trace_erofs_readpage(page, false); > f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT; > > + /* when trying to read beyond EOF, return zero page directly */ > + if (f.headoffset >= i_size_read(inode)) { > + zero_user_segment(page, 0, PAGE_SIZE); > + return 0; > + } Do we really need to optimize this rare case? I guess the follow readmore fix is enough, thoughts? Thanks, Gao Xiang