From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751941AbeBCKps (ORCPT ); Sat, 3 Feb 2018 05:45:48 -0500 Received: from omr-m006e.mx.aol.com ([204.29.186.6]:58367 "EHLO omr-m006e.mx.aol.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750821AbeBCKpl (ORCPT ); Sat, 3 Feb 2018 05:45:41 -0500 Subject: Re: [f2fs-dev] [PATCH] f2fs: fix to handle looped node chain during recovery From: Gao Xiang To: Chao Yu , jaegeuk@kernel.org, Yunlei He Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, "linux-fsdevel@vger.kernel.org" References: <20180203094439.3913-1-yuchao0@huawei.com> <6fe55970-6e30-d144-86d4-68d6fbd80cf3@aol.com> Message-ID: <3a4a4906-1f2a-197a-bfe1-f636f9b5243c@aol.com> Date: Sat, 3 Feb 2018 18:45:35 +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: <6fe55970-6e30-d144-86d4-68d6fbd80cf3@aol.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: 3039ac1a32ae5a7592d222a4 X-AOL-IP: 112.64.61.200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/2/3 18:35, Gao Xiang wrote: > 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". "B goes forward a step only when A goes forward 2(or constant x, more than 1) 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).... > Sorry, it seems the encoded diagram is in a mess, I try again. 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).... if B catchs up A, there exists a cycle. Thanks, > 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); >