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Date:   Mon, 23 Aug 2021 16:30:09 -0400
From:   Eric Whitney <enwlinux@gmail.com>
To:     Jeffle Xu <jefflexu@linux.alibaba.com>
Cc:     tytso@mit.edu, adilger.kernel@dilger.ca,
        linux-ext4@vger.kernel.org, joseph.qi@linux.alibaba.com,
        enwlinux@gmail.com, hsiangkao@linux.alibaba.com
Subject: Re: [PATCH v2] ext4: fix reserved space counter leakage
Message-ID: <20210823203009.GA10429@localhost.localdomain>
References: <20210823061358.84473-1-jefflexu@linux.alibaba.com>
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* 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>

Eric