Re: [PATCH v2 4/4] ocfs2: check/fix inode block for online file check

["Gang He" <ghe@suse.com>]

>>> 
> On 11/03/2015 04:47 PM, Gang He wrote:
>> 
>> 
>> 
>>>>>
>>> On 11/03/2015 04:15 PM, Gang He wrote:
>>>> Hello Junxiao,
>>>>
>>>> See my comments inline.
>>>>
>>>>
>>>>>>>
>>>>> Hi Gang,
>>>>>
>>>>> This is not like a right patch.
>>>>> First, online file check only checks inode's block number, valid flag,
>>>>> fs generation value, and meta ecc. I never see a real corruption
>>>>> happened only on this field, if these fields are corrupted, that means
>>>>> something bad may happen on other place. So fix this field may not help
>>>>> and even cause corruption more hard.
>>>> This online file check/fix feature is used to check/fix some light file meta 
> 
>>> block corruption, instead of turning a file system off and using fsck.ocfs2.
>>> What's light meta block corruption? Do you have a case about it?
>>>> e.g. meta ecc error, we really need not to use fsck.ocfs2. 
>>>> of course, this feature does not replace fsck.ocfs2 and touch some 
>>> complicated meta block problems, if there is some potential problem in some 
>>> areas, we can discuss them one by one.
>>>>
>>>>
>>>>
>>>>> Second, the repair way is wrong. In
>>>>> ocfs2_filecheck_repair_inode_block(), if these fields in disk don't
>>>>> match the ones in memory, the ones in memory are used to update the disk
>>>>> fields. The question is how do you know these field in memory are
>>>>> right(they may be the real corrupted ones)?
>>>> Here, if the inode block was corrupted, the file system is not able to load 
>>> it into the memory.
>>> How do you know inode block corrupted? If bh for inode block is
>>> overwritten, i mean bh corrupted, the repair will corrupted a good inode
>>> block.
>> You know, the meta block is only validated when the file system loads the 
> block from disk to memory.
>> If the inode object is in the memory, we consider this inode block is OK.
> This assuming is not true as there are always bugs. Bugs can make inode
> object in memory bad and corrupted the fs when repair the inode.
The inode object in the memory has probably been corrupted in some cases, right.
but in these cases, online file check/fix feature considers this inode object is validated, will not do any further modification and exit.
if the next corruption happens in case this inode is flushed into the disk, the bad thing is not made by online file check/fix code.
Next (maybe next mount), the inode block is reload into the memory by the file system will fail, with a kernel error log printing,
the online file check/fix probably can help to fix at this monent.

Thanks
Gang  
  
> 
> Thanks,
> Junxiao.
>> If the inode is not loaded by the file system via the normal way, the file 
> system will print a kernel error log to tell which ino is corrupted.
>> we will use  ocfs2_filecheck_repair_inode_block() function to fix the inode 
> block before loading.
>> 
>> Thanks
>> Gang
>> 
>>>
>>> Thanks,
>>> Junxiao.
>>>
>>>> ocfs2_filecheck_repair_inode_block() will able to load it into the memory, 
>>> since it try to fix these light-level problem before loading.
>>>> if the fix is OK, the changed meta-block can pass the block-validate function 
>>> and load into the memory as a inode object.
>>>> Since the file system is under a cluster environment, we have to use some 
>>> existing function and code path to keep these block operation under a 
> cluster 
>>> lock.
>>>>
>>>>
>>>> Thanks
>>>> Gang
>>>>
>>>>>
>>>>> Thanks,
>>>>> Junxiao.
>>>>> On 10/28/2015 02:26 PM, Gang He wrote:
>>>>>> +static int ocfs2_filecheck_repair_inode_block(struct super_block *sb,
>>>>>> +			       struct buffer_head *bh)
>>>>>> +{
>>>>>> +	int rc;
>>>>>> +	int changed = 0;
>>>>>> +	struct ocfs2_dinode *di = (struct ocfs2_dinode *)bh->b_data;
>>>>>> +
>>>>>> +	rc = ocfs2_filecheck_validate_inode_block(sb, bh);
>>>>>> +	/* Can't fix invalid inode block */
>>>>>> +	if (!rc || rc == -OCFS2_FILECHECK_ERR_INVALIDINO)
>>>>>> +		return rc;
>>>>>> +
>>>>>> +	trace_ocfs2_filecheck_repair_inode_block(
>>>>>> +		(unsigned long long)bh->b_blocknr);
>>>>>> +
>>>>>> +	if (ocfs2_is_hard_readonly(OCFS2_SB(sb)) ||
>>>>>> +		ocfs2_is_soft_readonly(OCFS2_SB(sb))) {
>>>>>> +		mlog(ML_ERROR,
>>>>>> +			"Filecheck: try to repair dinode #%llu on readonly filesystem\n",
>>>>>> +			(unsigned long long)bh->b_blocknr);
>>>>>> +		return -OCFS2_FILECHECK_ERR_READONLY;
>>>>>> +	}
>>>>>> +
>>>>>> +	if (le64_to_cpu(di->i_blkno) != bh->b_blocknr) {
>>>>>> +		di->i_blkno = cpu_to_le64(bh->b_blocknr);
>>>>>> +		changed = 1;
>>>>>> +		mlog(ML_ERROR,
>>>>>> +			"Filecheck: reset dinode #%llu: i_blkno to %llu\n",
>>>>>> +			(unsigned long long)bh->b_blocknr,
>>>>>> +			(unsigned long long)le64_to_cpu(di->i_blkno));
>>>>>> +	}
>>>>>> +
>>>>>> +	if (!(di->i_flags & cpu_to_le32(OCFS2_VALID_FL))) {
>>>>>> +		di->i_flags |= cpu_to_le32(OCFS2_VALID_FL);
>>>>>> +		changed = 1;
>>>>>> +		mlog(ML_ERROR,
>>>>>> +			"Filecheck: reset dinode #%llu: OCFS2_VALID_FL is set\n",
>>>>>> +			(unsigned long long)bh->b_blocknr);
>>>>>> +	}
>>>>>> +
>>>>>> +	if (le32_to_cpu(di->i_fs_generation) !=
>>>>>> +	    OCFS2_SB(sb)->fs_generation) {
>>>>>> +		di->i_fs_generation = cpu_to_le32(OCFS2_SB(sb)->fs_generation);
>>>>>> +		changed = 1;
>>>>>> +		mlog(ML_ERROR,
>>>>>> +			"Filecheck: reset dinode #%llu: fs_generation to %u\n",
>>>>>> +			(unsigned long long)bh->b_blocknr,
>>>>>> +			le32_to_cpu(di->i_fs_generation));
>>>>>> +	}
>>>>>> +
>>>>>> +	if (changed ||
>>>>>> +		ocfs2_validate_meta_ecc(sb, bh->b_data, &di->i_check)) {
>>>>>> +		ocfs2_compute_meta_ecc(sb, bh->b_data, &di->i_check);
>>>>>> +		mark_buffer_dirty(bh);
>>>>>> +		mlog(ML_ERROR,
>>>>>> +			"Filecheck: reset dinode #%llu: compute meta ecc\n",
>>>>>> +			(unsigned long long)bh->b_blocknr);
>>>>>> +	}
>>>>>> +
>>>>>> +	return 0;
>>>>>> +}
>>>>