From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.cn.fujitsu.com ([183.91.158.132]:9513 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726905AbeINMTT (ORCPT ); Fri, 14 Sep 2018 08:19:19 -0400 Subject: Re: [PATCH v2 4/7] btrfs-progs: lowmem: search key of root again after check_fs_root() under repair To: Nikolay Borisov , Qu Wenruo , , References: <20180912204924.10089-1-suy.fnst@cn.fujitsu.com> <20180912204924.10089-5-suy.fnst@cn.fujitsu.com> <070c1e5b-1ce8-f69a-fc49-426d51d5703b@gmx.com> <8572ed9f-3b9d-9df2-b596-d3362fc9b8f2@suse.com> From: Su Yue Message-ID: Date: Fri, 14 Sep 2018 15:13:05 +0800 MIME-Version: 1.0 In-Reply-To: <8572ed9f-3b9d-9df2-b596-d3362fc9b8f2@suse.com> Content-Type: text/plain; charset="utf-8"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 09/14/2018 02:27 PM, Nikolay Borisov wrote: > > > On 14.09.2018 03:58, Su Yue wrote: >> >> >> On 09/14/2018 07:37 AM, Qu Wenruo wrote: >>> >>> >>> On 2018/9/13 上午4:49, damenly.su@gmail.com wrote: >>>> From: Su Yue >>>> >>>> In check_fs_roots_lowmem(), we do search and follow the resulted path >>>> to call check_fs_root(), then call btrfs_next_item() to check next >>>> root. >>>> However, if repair is enabled, the root tree can be cowed, the >>>> existed path can cause strange errors. >>>> >>>> Solution: >>>>    If repair, save the key before calling check_fs_root, >>>>    search the saved key again before checking next root. >>> >>> Both reason and solution looks good. >>> >>>> >>>> Signed-off-by: Su Yue >>>> --- >>>>   check/mode-lowmem.c | 15 +++++++++++++++ >>>>   1 file changed, 15 insertions(+) >>>> >>>> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c >>>> index 89a304bbdd69..8fc9edab1d66 100644 >>>> --- a/check/mode-lowmem.c >>>> +++ b/check/mode-lowmem.c >>>> @@ -4967,9 +4967,13 @@ int check_fs_roots_lowmem(struct btrfs_fs_info >>>> *fs_info) >>>>       } >>>>         while (1) { >>>> +        struct btrfs_key saved_key; >>>> + >>>>           node = path.nodes[0]; >>>>           slot = path.slots[0]; >>>>           btrfs_item_key_to_cpu(node, &key, slot); >>>> +        if (repair) >>>> +            saved_key = key; >>>>           if (key.objectid > BTRFS_LAST_FREE_OBJECTID) >>>>               goto out; >>>>           if (key.type == BTRFS_ROOT_ITEM_KEY && >>>> @@ -5000,6 +5004,17 @@ int check_fs_roots_lowmem(struct btrfs_fs_info >>>> *fs_info) >>>>               err |= ret; >>>>           } >>>>   next: >>>> +        /* >>>> +         * Since root tree can be cowed during repair, >>>> +         * here search the saved key again. >>>> +         */ >>>> +        if (repair) { >>>> +            btrfs_release_path(&path); >>>> +            ret = btrfs_search_slot(NULL, fs_info->tree_root, >>>> +                        &saved_key, &path, 0, 0); >>>> +            /* Repair never deletes trees, search must succeed. */ >>>> +            BUG_ON(ret); >>> >>> But this doesn't look good to me. >>> >>> Your assumption here is valid (at least for now), but it's possible that >>> some tree blocks get corrupted in a large root tree, and in that case, >>> we could still read part of the root tree, but btrfs_search_slot() could >>> still return -EIO for certain search key. >>> >>> So I still prefer to do some error handling other than BUG_ON(ret). >>> >> Okay, will try it. > > Just to emphasize Qu's point - we should strive to remove existing > BUG_ON and should never introduce new ones. btrfs-progs is already quite > messy and we should be improving that. > Understood, thanks for your emphasis． Su >> >> Thanks, >> Su >>> Thanks, >>> Qu >>> >>>> +        } >>>>           ret = btrfs_next_item(tree_root, &path); >>>>           if (ret > 0) >>>>               goto out; >>>> >>> >>> >> >> >> > >