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Subject: Re: [PATCH v2] ext4: fix reserved space counter leakage
From:   JeffleXu <jefflexu@linux.alibaba.com>
To:     Eric Whitney <enwlinux@gmail.com>
Cc:     tytso@mit.edu, adilger.kernel@dilger.ca,
        linux-ext4@vger.kernel.org, joseph.qi@linux.alibaba.com,
        hsiangkao@linux.alibaba.com
References: <20210823061358.84473-1-jefflexu@linux.alibaba.com>
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 <77ac5ffe-9769-bcb4-0600-f72ddf0aa59a@linux.alibaba.com>
Message-ID: <ffb203e9-b8b6-d3fe-a438-4dbddf6f7938@linux.alibaba.com>
Date:   Mon, 6 Sep 2021 14:46:16 +0800
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On 8/25/21 9:38 AM, JeffleXu wrote:
> 
> 
> On 8/24/21 4:30 AM, Eric Whitney wrote:
>> * Jeffle Xu <jefflexu@linux.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@vger.kernel.org>
>>> Suggested-by: Gao Xiang <hsiangkao@linux.alibaba.com>
>>> Signed-off-by: Jeffle Xu <jefflexu@linux.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@gmail.com>
> 
> 
> Hi tytso, it's a bug fix and it would be great if it could be merged to
> 5.15.
> 

ping ...

-- 
Thanks,
Jeffle