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

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Date:   Tue, 20 Jul 2021 08:04:35 +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 2021/7/20 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?

Thanks,

> 
>>   		goto stop;
>> +	}
>>
>>   	f2fs_flush_sit_entries(sbi, cpc);
>>
>> @@ -1648,10 +1650,12 @@ int f2fs_write_checkpoint(struct f2fs_sb_info *sbi, struct cp_control *cpc)
>>   	f2fs_save_inmem_curseg(sbi);
>>
>>   	err = do_checkpoint(sbi, cpc);
>> -	if (err)
>> +	if (err) {
>> +		f2fs_stop_checkpoint(sbi, false);
>>   		f2fs_release_discard_addrs(sbi);
>> -	else
>> +	} else {
>>   		f2fs_clear_prefree_segments(sbi, cpc);
>> +	}
>>
>>   	f2fs_restore_inmem_curseg(sbi);
>>   stop:
>> -- 
>> 2.22.1