linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: reset free segment to prefree status when do

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Message-ID: <3d3ef5c9-fbb6-df85-26f7-e493da594b22@kernel.org>
Date:   Tue, 3 Aug 2021 09:00:57 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Yangtao Li <frank.li@...o.com>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: reset free segment to prefree status
 when do_checkpoint() fail

On 2021/8/3 1:59, Jaegeuk Kim wrote:
> On 08/01, Chao Yu wrote:
>> On 2021/7/31 6:18, Jaegeuk Kim wrote:
>>> On 07/20, Chao Yu wrote:
>>>> On 2021/7/20 2:25, Jaegeuk Kim wrote:
>>>>> On 07/19, Chao Yu wrote:
>>>>>> On 2021/4/27 20:37, Chao Yu wrote:
>>>>>>> I think just reverting dirty/free bitmap is not enough if checkpoint fails,
>>>>>>> due to we have updated sbi->cur_cp_pack and nat/sit bitmap, next CP tries
>>>>>>> to overwrite last valid meta/node/data, then filesystem will be corrupted.
>>>>>>>
>>>>>>> So I suggest to set cp_error if do_checkpoint() fails until we can handle
>>>>>>> all cases, which is not so easy.
>>>>>>>
>>>>>>> How do you think?
>>>>>>
>>>>>> Let's add below patch first before you figure out the patch which covers all
>>>>>> things.
>>>>>>
>>>>>>    From 3af957c98e9e04259f8bb93ca0b74ba164f3f27e Mon Sep 17 00:00:00 2001
>>>>>> From: Chao Yu <chao@...nel.org>
>>>>>> Date: Mon, 19 Jul 2021 16:37:44 +0800
>>>>>> Subject: [PATCH] f2fs: fix to stop filesystem update once CP failed
>>>>>>
>>>>>> During f2fs_write_checkpoint(), once we failed in
>>>>>> f2fs_flush_nat_entries() or do_checkpoint(), metadata of filesystem
>>>>>> such as prefree bitmap, nat/sit version bitmap won't be recovered,
>>>>>> it may cause f2fs image to be inconsistent, let's just set CP error
>>>>>> flag to avoid further updates until we figure out a scheme to rollback
>>>>>> all metadatas in such condition.
>>>>>>
>>>>>> Reported-by: Yangtao Li <frank.li@...o.com>
>>>>>> Signed-off-by: Yangtao Li <frank.li@...o.com>
>>>>>> Signed-off-by: Chao Yu <chao@...nel.org>
>>>>>> ---
>>>>>>     fs/f2fs/checkpoint.c | 10 +++++++---
>>>>>>     1 file changed, 7 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>>>>> index 6c208108d69c..096c85022f62 100644
>>>>>> --- a/fs/f2fs/checkpoint.c
>>>>>> +++ b/fs/f2fs/checkpoint.c
>>>>>> @@ -1639,8 +1639,10 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>>>>>
>>>>>>     	/* write cached NAT/SIT entries to NAT/SIT area */
>>>>>>     	err = f2fs_flush_nat_entries(sbi, cpc);
>>>>>> -	if (err)
>>>>>> +	if (err) {
>>>>>> +		f2fs_stop_checkpoint(sbi, false);
>>>>>
>>>>> I think we should abuse this, since we can get any known ENOMEM as well.
>>>>
>>>> Yup, but one critical issue here is it can break A/B update of NAT area,
>>>> so, in order to fix this hole, how about using NOFAIL memory allocation
>>>> in f2fs_flush_nat_entries() first until we figure out the finial scheme?
>>>
>>> NOFAIL is risky, so how about adding a retry logic on ENOMEM with a message
>>> and then giving up if we can't get the memory? BTW, what about EIO or other
>>> family?
>>
>> How about this?
> 
> Hmm, it seems we won't get ENOMEM.
> 
> __flush_nat_entry_set
>   -> get_next_nat_page
>     -> ...
>      -> __get_meta_page
>        -> repeat on ENOMEM, but stop_checkpoint on EIO

Correct, I missed to check __get_meta_page() and f2fs_get_meta_page_retry().

> 
> If we have an error here, we should have stopped checkpoint. Have you seen other
> issue?

Still we should fix the case from below path?

- f2fs_write_checkpoint
  - do_checkpoint
   - f2fs_flush_device_cache failed

Thanks,