From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751725AbeBCKgG (ORCPT ); Sat, 3 Feb 2018 05:36:06 -0500 Received: from omr-m003e.mx.aol.com ([204.29.186.3]:36357 "EHLO omr-m003e.mx.aol.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750741AbeBCKf6 (ORCPT ); Sat, 3 Feb 2018 05:35:58 -0500 Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to handle looped node chain during recovery To: Chao Yu , jaegeuk@kernel.org, Yunlei He Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net References: <20180203094439.3913-1-yuchao0@huawei.com> From: Gao Xiang Message-ID: <6fe55970-6e30-d144-86d4-68d6fbd80cf3@aol.com> Date: Sat, 3 Feb 2018 18:35:53 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180203094439.3913-1-yuchao0@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US x-aol-global-disposition: G x-aol-sid: 3039ac1addcd5a75908b1a1a X-AOL-IP: 112.64.61.200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Chao and YunLei, On 2018/2/3 17:44, Chao Yu wrote: > There is no checksum in node block now, so bit-transition from hardware > can make node_footer.next_blkaddr being corrupted w/o any detection, > result in node chain becoming looped one. > > For this condition, during recovery, in order to avoid running into dead > loop, let's detect it and just skip out. > > Signed-off-by: Yunlei He > Signed-off-by: Chao Yu > --- > fs/f2fs/recovery.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c > index b6d1ec620a8c..60dd0cee4820 100644 > --- a/fs/f2fs/recovery.c > +++ b/fs/f2fs/recovery.c > @@ -243,6 +243,9 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head, > struct curseg_info *curseg; > struct page *page = NULL; > block_t blkaddr; > + unsigned int loop_cnt = 0; > + unsigned int free_blocks = sbi->user_block_count - > + valid_user_blocks(sbi); There exists another way to detect loop more faster but only using two variables. The algorithm is described as simply "B goes forward a steps only A goes forwards 2 steps". For example: 1)    1   2  3  4   5   6     7    |             \             /    |                \------/   A, B 2)    1  2  3  4   5   6     7     |   |        \             /    B   A        \------/  3)    1  2  3  4   5   6     7        |    |     \             /       B   A      \------/   4)    1  2  3  4   5   6     7        |       |\             /       B      A \------/ 5).... B will equal A or beyoud A if and only if there has a cycle. It's a more faster algorithm. :D Thanks, > int err = 0; > > /* get node pages in the current segment */ > @@ -295,6 +298,17 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head, > if (IS_INODE(page) && is_dent_dnode(page)) > entry->last_dentry = blkaddr; > next: > + /* sanity check in order to detect looped node chain */ > + if (++loop_cnt >= free_blocks || > + blkaddr == next_blkaddr_of_node(page)) { > + f2fs_msg(sbi->sb, KERN_NOTICE, > + "%s: detect looped node chain, " > + "blkaddr:%u, next:%u", > + __func__, blkaddr, next_blkaddr_of_node(page)); > + err = -EINVAL; > + break; > + } > + > /* check next segment */ > blkaddr = next_blkaddr_of_node(page); > f2fs_put_page(page, 1);