linux-ext4 - Re: [PATCH v4 1/2] ext4: fix inode tree inconsistency caused by ENOMEM in ext4_split_extent

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Date:   Wed, 15 Feb 2023 16:51:23 +0800
From:   zhanchengbin <zhanchengbin1@...wei.com>
To:     Jan Kara <jack@...e.cz>
CC:     <tytso@....edu>, <jack@...e.com>, <linux-ext4@...r.kernel.org>,
        <yi.zhang@...wei.com>, <linfeilong@...wei.com>,
        <liuzhiqiang26@...wei.com>
Subject: Re: [PATCH v4 1/2] ext4: fix inode tree inconsistency caused by
 ENOMEM in ext4_split_extent_at


On 2023/2/14 19:48, Jan Kara wrote:
> On Mon 13-02-23 12:05:21, zhanchengbin wrote:
>> If ENOMEM fails when the extent is splitting, we need to restore the length
>> of the split extent.
>> In the call stack of the ext4_split_extent_at function, only in
>> ext4_ext_create_new_leaf will it alloc memory and change the shape of the
>> extent tree,even if an ENOMEM is returned at this time, the extent tree is
>> still self-consistent, Just restore the split extent lens in the function
>> ext4_split_extent_at.
>>
>> ext4_split_extent_at
>>   ext4_ext_insert_extent
>>    ext4_ext_create_new_leaf
>>     1)ext4_ext_split
>>       ext4_find_extent
>>     2)ext4_ext_grow_indepth
>>       ext4_find_extent
>>
>> Signed-off-by: zhanchengbin <zhanchengbin1@...wei.com>
>> ---
>>   fs/ext4/extents.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index 9de1c9d1a13d..0f95e857089e 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -935,6 +935,7 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
>>   
>>   		bh = read_extent_tree_block(inode, path[ppos].p_idx, --i, flags);
>>   		if (IS_ERR(bh)) {
>> +			EXT4_ERROR_INODE(inode, "IO error reading extent block");
> 
> Why have you added this? Usually we don't log any additional errors for IO
> errors because the storage layer already reports it... Furthermore this
> would potentialy panic the system / remount the fs RO which we also usually
> don't do in case of IO errors, only in case of FS corruption.
> 
> 								Honza

Because failure of read_extent_tree_block indirectly leads to filesystem
inconsistency in ext4_split_extent_at, I want the filesystem to become
read-only after failure.

  - bin.

> 
>>   			ret = PTR_ERR(bh);
>>   			goto err;
>>   		}
>> @@ -3251,7 +3252,7 @@ static int ext4_split_extent_at(handle_t *handle,
>>   		ext4_ext_mark_unwritten(ex2);
>>   
>>   	err = ext4_ext_insert_extent(handle, inode, ppath, &newex, flags);
>> -	if (err != -ENOSPC && err != -EDQUOT)
>> +	if (err != -ENOSPC && err != -EDQUOT && err != -ENOMEM)
>>   		goto out;
>>   
>>   	if (EXT4_EXT_MAY_ZEROOUT & split_flag) {
>> -- 
>> 2.31.1
>>