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=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 76E42C433E6 for ; Fri, 19 Mar 2021 02:16:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47E64614A7 for ; Fri, 19 Mar 2021 02:16:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230375AbhCSCPa (ORCPT ); Thu, 18 Mar 2021 22:15:30 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:13199 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229736AbhCSCP0 (ORCPT ); Thu, 18 Mar 2021 22:15:26 -0400 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4F1nVK65MjzmXLp; Fri, 19 Mar 2021 10:12:57 +0800 (CST) Received: from [10.136.110.154] (10.136.110.154) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.498.0; Fri, 19 Mar 2021 10:15:19 +0800 Subject: Re: [PATCH v2] erofs: fix bio->bi_max_vecs behavior change To: Gao Xiang , , Chao Yu CC: , Gao Xiang , "Martin DEVERA" References: <20210306033109.28466-1-hsiangkao@aol.com> <20210306040438.8084-1-hsiangkao@aol.com> From: Chao Yu Message-ID: Date: Fri, 19 Mar 2021 10:15:18 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20210306040438.8084-1-hsiangkao@aol.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.136.110.154] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/3/6 12:04, Gao Xiang wrote: > From: Gao Xiang > > Martin reported an issue that directory read could be hung on the > latest -rc kernel with some certain image. The root cause is that > commit baa2c7c97153 ("block: set .bi_max_vecs as actual allocated > vector number") changes .bi_max_vecs behavior. bio->bi_max_vecs > is set as actual allocated vector number rather than the requested > number now. > > Let's avoid using .bi_max_vecs completely instead. > > Reported-by: Martin DEVERA > Signed-off-by: Gao Xiang > --- > change since v1: > - since bio->bi_max_vecs doesn't record extent blocks anymore, > introduce a remaining extent block to avoid extent excess. > > fs/erofs/data.c | 28 +++++++++++----------------- > 1 file changed, 11 insertions(+), 17 deletions(-) > > diff --git a/fs/erofs/data.c b/fs/erofs/data.c > index f88851c5c250..1249e74b3bf0 100644 > --- a/fs/erofs/data.c > +++ b/fs/erofs/data.c > @@ -129,6 +129,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > struct page *page, > erofs_off_t *last_block, > unsigned int nblocks, > + unsigned int *eblks, > bool ra) > { > struct inode *const inode = mapping->host; > @@ -145,8 +146,7 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > > /* note that for readpage case, bio also equals to NULL */ > if (bio && > - /* not continuous */ > - *last_block + 1 != current_block) { > + (*last_block + 1 != current_block || !*eblks)) { Xiang, I found below function during checking bi_max_vecs usage in f2fs: /** * bio_full - check if the bio is full * @bio: bio to check * @len: length of one segment to be added * * Return true if @bio is full and one segment with @len bytes can't be * added to the bio, otherwise return false */ static inline bool bio_full(struct bio *bio, unsigned len) { if (bio->bi_vcnt >= bio->bi_max_vecs) return true; if (bio->bi_iter.bi_size > UINT_MAX - len) return true; return false; } Could you please check that whether it will be better to use bio_full() rather than using left-space-in-bio maintained by erofs itself? something like: if (bio && (bio_full(bio, PAGE_SIZE) || /* not continuous */ (*last_block + 1 != current_block)) I'm thinking we need to decouple bio detail implementation as much as possible, to avoid regression whenever bio used/max size definition updates, though I've no idea how to fix f2fs case. Let me know if you have other concern. Thanks, > submit_bio_retry: > submit_bio(bio); > bio = NULL; > @@ -216,7 +216,8 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > if (nblocks > DIV_ROUND_UP(map.m_plen, PAGE_SIZE)) > nblocks = DIV_ROUND_UP(map.m_plen, PAGE_SIZE); > > - bio = bio_alloc(GFP_NOIO, bio_max_segs(nblocks)); > + *eblks = bio_max_segs(nblocks); > + bio = bio_alloc(GFP_NOIO, *eblks); > > bio->bi_end_io = erofs_readendio; > bio_set_dev(bio, sb->s_bdev); > @@ -229,16 +230,8 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > /* out of the extent or bio is full */ > if (err < PAGE_SIZE) > goto submit_bio_retry; > - > + --*eblks; > *last_block = current_block; > - > - /* shift in advance in case of it followed by too many gaps */ > - if (bio->bi_iter.bi_size >= bio->bi_max_vecs * PAGE_SIZE) { > - /* err should reassign to 0 after submitting */ > - err = 0; > - goto submit_bio_out; > - } > - > return bio; > > err_out: > @@ -252,7 +245,6 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > > /* if updated manually, continuous pages has a gap */ > if (bio) > -submit_bio_out: > submit_bio(bio); > return err ? ERR_PTR(err) : NULL; > } > @@ -264,23 +256,26 @@ static inline struct bio *erofs_read_raw_page(struct bio *bio, > static int erofs_raw_access_readpage(struct file *file, struct page *page) > { > erofs_off_t last_block; > + unsigned int eblks; > struct bio *bio; > > trace_erofs_readpage(page, true); > > bio = erofs_read_raw_page(NULL, page->mapping, > - page, &last_block, 1, false); > + page, &last_block, 1, &eblks, false); > > if (IS_ERR(bio)) > return PTR_ERR(bio); > > - DBG_BUGON(bio); /* since we have only one bio -- must be NULL */ > + if (bio) > + submit_bio(bio); > return 0; > } > > static void erofs_raw_access_readahead(struct readahead_control *rac) > { > erofs_off_t last_block; > + unsigned int eblks; > struct bio *bio = NULL; > struct page *page; > > @@ -291,7 +286,7 @@ static void erofs_raw_access_readahead(struct readahead_control *rac) > prefetchw(&page->flags); > > bio = erofs_read_raw_page(bio, rac->mapping, page, &last_block, > - readahead_count(rac), true); > + readahead_count(rac), &eblks, true); > > /* all the page errors are ignored when readahead */ > if (IS_ERR(bio)) { > @@ -305,7 +300,6 @@ static void erofs_raw_access_readahead(struct readahead_control *rac) > put_page(page); > } > > - /* the rare case (end in gaps) */ > if (bio) > submit_bio(bio); > } >