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Date:   Wed, 25 Aug 2021 09:38:05 +0800
From:   JeffleXu <jefflexu@...ux.alibaba.com>
To:     Eric Whitney <enwlinux@...il.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, joseph.qi@...ux.alibaba.com,
        hsiangkao@...ux.alibaba.com
Subject: Re: [PATCH v2] ext4: fix reserved space counter leakage



On 8/24/21 4:30 AM, Eric Whitney wrote:
> * Jeffle Xu <jefflexu@...ux.alibaba.com>:
>> When ext4_insert_delayed block receives and recovers from an error from
>> ext4_es_insert_delayed_block(), e.g., ENOMEM, it does not release the
>> space it has reserved for that block insertion as it should. One effect
>> of this bug is that s_dirtyclusters_counter is not decremented and
>> remains incorrectly elevated until the file system has been unmounted.
>> This can result in premature ENOSPC returns and apparent loss of free
>> space.
>>
>> Another effect of this bug is that
>> /sys/fs/ext4/<dev>/delayed_allocation_blocks can remain non-zero even
>> after syncfs has been executed on the filesystem.
>>
>> Besides, add check for s_dirtyclusters_counter when inode is going to be
>> evicted and freed. s_dirtyclusters_counter can still keep non-zero until
>> inode is written back in .evict_inode(), and thus the check is delayed
>> to .destroy_inode().
>>
>> Fixes: 51865fda28e5 ("ext4: let ext4 maintain extent status tree")
>> Cc: <stable@...r.kernel.org>
>> Suggested-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
>> Signed-off-by: Jeffle Xu <jefflexu@...ux.alibaba.com>
>> ---
>> changes since v1:
>> - improve commit log suggested by Eric Whitney
>> - update "Suggested-by" title for Gao Xian, who actually found this bug
>>   code
>> - add check for s_dirtyclusters_counter in .destroy_inode()
>> ---
>>  fs/ext4/inode.c | 5 +++++
>>  fs/ext4/super.c | 6 ++++++
>>  2 files changed, 11 insertions(+)
>>
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index d8de607849df..73daf9443e5e 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -1640,6 +1640,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>  	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>  	int ret;
>>  	bool allocated = false;
>> +	bool reserved = false;
>>  
>>  	/*
>>  	 * If the cluster containing lblk is shared with a delayed,
>> @@ -1656,6 +1657,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>  		ret = ext4_da_reserve_space(inode);
>>  		if (ret != 0)   /* ENOSPC */
>>  			goto errout;
>> +		reserved = true;
>>  	} else {   /* bigalloc */
>>  		if (!ext4_es_scan_clu(inode, &ext4_es_is_delonly, lblk)) {
>>  			if (!ext4_es_scan_clu(inode,
>> @@ -1668,6 +1670,7 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>  					ret = ext4_da_reserve_space(inode);
>>  					if (ret != 0)   /* ENOSPC */
>>  						goto errout;
>> +					reserved = true;
>>  				} else {
>>  					allocated = true;
>>  				}
>> @@ -1678,6 +1681,8 @@ static int ext4_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk)
>>  	}
>>  
>>  	ret = ext4_es_insert_delayed_block(inode, lblk, allocated);
>> +	if (ret && reserved)
>> +		ext4_da_release_space(inode, 1);
>>  
>>  errout:
>>  	return ret;
>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>> index dfa09a277b56..61bf52b58fca 100644
>> --- a/fs/ext4/super.c
>> +++ b/fs/ext4/super.c
>> @@ -1351,6 +1351,12 @@ static void ext4_destroy_inode(struct inode *inode)
>>  				true);
>>  		dump_stack();
>>  	}
>> +
>> +	if (EXT4_I(inode)->i_reserved_data_blocks)
>> +		ext4_msg(inode->i_sb, KERN_ERR,
>> +			 "Inode %lu (%p): i_reserved_data_blocks (%u) not cleared!",
>> +			 inode->i_ino, EXT4_I(inode),
>> +			 EXT4_I(inode)->i_reserved_data_blocks);
>>  }
>>  
>>  static void init_once(void *foo)
>> -- 
>> 2.27.0
>>
> 
> Looks good, passed 4k xfstests-bld regression.  Feel free to add:
> 
> Reviewed-by: Eric Whitney <enwlinux@...il.com>


Hi tytso, it's a bug fix and it would be great if it could be merged to
5.15.

-- 
Thanks,
Jeffle

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