Message-ID: <f49c2ff5-d02e-e5ee-7e6f-dfa2edea905a@huawei.com>
Date:   Fri, 25 Aug 2023 21:15:02 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <linux-ext4@...r.kernel.org>, <tytso@....edu>,
        <adilger.kernel@...ger.ca>, <darrick.wong@...cle.com>,
        <yi.zhang@...wei.com>, <yangerkun@...wei.com>,
        <yukuai3@...wei.com>, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH] e2fsck: delay quotas loading in release_orphan_inodes()

On 2023/8/25 20:50, Jan Kara wrote:
> On Fri 25-08-23 10:08:17, Baokun Li wrote:
>> On 2023/8/25 3:37, Jan Kara wrote:
>>> On Thu 24-08-23 20:56:14, Baokun Li wrote:
>>>> On 2023/8/24 18:08, Jan Kara wrote:
>>>>> On Thu 24-08-23 10:27:46, Baokun Li wrote:
>>>>>> Hello, Jan!
>>>>>>
>>>>>> On 2023/8/24 1:05, Jan Kara wrote:
>>>>>>> On Thu 17-08-23 16:18:28, Baokun Li wrote:
>>>>>>>> After 7d79b40b ("e2fsck: adjust quota counters when clearing orphaned
>>>>>>>> inodes"), we load all the quotas before we process the orphaned inodes,
>>>>>>>> and when we load the quotas, we check the checsum of the bbitmap for each
>>>>>>>> group. If one of the bbitmap checksums is wrong, the following error will
>>>>>>>> be reported:
>>>>>>>>
>>>>>>>> “Error initializing quota context in support library:
>>>>>>>>      Block bitmap checksum does not match bitmap”
>>>>>>>>
>>>>>>>> But loading quotas comes before checking the current superblock for the
>>>>>>>> EXT2_ERROR_FS flag, which makes it impossible to use e2fsck to repair any
>>>>>>>> image that contains orphan inodes and has the wrong bbitmap checksum.
>>>>>>>> So delaying quota loading until after the EXT2_ERROR_FS judgment avoids
>>>>>>>> the above problem.
>>>>>>>>
>>>>>>>> Signed-off-by: Baokun Li <libaokun1@...wei.com>
>>>>>>> This certainly looks better but I wonder if there still isn't a problem if
>>>>>>> the bitmap checksums are wrong but EXT2_ERROR_FS is not set. Shouldn't we
>>>>>>> rather move the initialization of the quota files after the call to
>>>>>>> e2fsck_read_bitmaps()?
>>>>>>>
>>>>>>> 								Honza
>>>>>> When the bitmap checksums are wrong but EXT2_ERROR_FS is not set, we must
>>>>>> have lost some data (error flag or group descriptor or bitmap), so there
>>>>>> is something wrong with the kernel at this time, so I don't think we
>>>>>> should fix the image directly, but rather let the user realize that
>>>>>> something is wrong with the filesystem logic.
>>>>> I agree it means there is a problem somewhere (the storage, the kernel, or
>>>>> similar). But just ignoring bitmap checksums in release_orphan_inodes() is
>>>>> exactly how e2fsck behaves on filesystems without quota feature so I see no
>>>>> reason for quota feature to change that because the inconsistency has
>>>>> nothing to do with quotas...
>>>>>
>>>>>> Moreover, if we don't care how this happened, but just want to fix the
>>>>>> image, we only need to run "e2fsck -a" twice. After merging in the
>>>>>> current patch, we always empty the orphan list before loading the quotas,
>>>>>> and EXT2_ERROR_FS is set when loading the quotas fails, so this will be
>>>>>> fixed the second time you run e2fsck. It will not happen that every
>>>>>> e2fsck will fail like it did before.
>>>>> I see, you're right so it isn't as bad as I originally thought but still my
>>>>> argument above holds - IMO e2fsck should treat wrong bitmap checksums the
>>>>> same way with and without the quota feature.
>>>>>
>>>>> 								Honza
>>>> The original flow that went wrong here is as follows：
>>>> e2fsck
>>>>    e2fsck_run_ext3_journal
>>>>    check_super_block
>>>>     release_orphan_inodes
>>>>      e2fsck_read_all_quotas
>>>>       quota_read_all_dquots
>>>>        quota_file_open
>>>>         ext2fs_read_bitmaps
>>>>          ext2fs_rw_bitmaps
>>>>           read_bitmaps_range
>>>>            read_bitmaps_range_start
>>>>             ext2fs_block_bitmap_csum_verify
>>>>              !!! error
>>>>    e2fsck_run
>>>>
>>>> Yes, the inconsistency has nothing to do with quota, but quota is loaded
>>>> here to keep track of space changes during the normal processing of
>>>> orphan list. If quota was not loaded, we would not have read and check
>>>> bitmaps until Pass5, and we had already done a lot of checking and
>>>> tweaking of inodes, blocks, and dirs before Pass5, and the bitmaps
>>>> inconsistency may have been fixed during that time.
>>> This is not true. release_orphan_inodes() calls e2fsck_read_bitmaps() which
>>> loads all the bitmaps while ignoring checksum failures. This is needed so
>>> that blocks released during orphan cleanup are properly tracked as free.
>>> All I want to do is to move the call to e2fsck_read_all_quotas() a bit
>>> further than you moved it to a place after the e2fsck_read_bitmaps()
>>> call...
>> Yes, e2fsck_read_bitmaps() ignores checksum errors for reading bitmaps,
>> which prevents us from exiting e2fsck due to checksum error in
>> release_orphan_inodes(), but in the case of the previously mentioned
>> checksum error but EXT2_ERROR_FS is not set, when we execute "e2fsck -a",
>> since checksum is ignored, the filesystem is considered clean, so it
>> exits e2fsck without performing a force check, but the error is still
>> there.
> Yes, and I believe that is a correct behavior because "e2fsck -a" means
> "don't check the filesystem unless it is required" - i.e., too long since the
> last check, too many mounts, or errors detected state. And if the
> filesystem doesn't have the quota feature, this is indeed what is going to
> happen. We'll happily skip the filesystem with bitmap checksum errors. So
> why should we complain about it when quota feature is enabled?
>
> If you think bitmap checksums should be checked by e2fsck -a, then we can
> have that discussion (separate patch from your quota fixup) but then it
> should happen regardless of the quota feature. Because doing it only with
> quota feature enabled is really unexpected and is going to confuse users.
>
> 								Honza

Got it!

We didn't care about bitmap checksum errors before Pass5, so it's as 
expected

to ignore them!  Thank you for your patient explanation!

I'll update the patch with your suggestion in the next version!


Thanks!
-- 
With Best Regards,
Baokun Li
.

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