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Date:   Mon, 20 Sep 2021 15:58:16 +0200
From:   Jan Kara <jack@...e.cz>
To:     Zhang Yi <yi.zhang@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, yukuai3@...wei.com
Subject: Re: [PATCH v5 3/3] ext4: prevent getting empty inode buffer

On Wed 01-09-21 10:09:55, Zhang Yi wrote:
> In ext4_get_inode_loc(), we may skip IO and get an zero && uptodate
> inode buffer when the inode monopolize an inode block for performance
> reason. For most cases, ext4_mark_iloc_dirty() will fill the inode
> buffer to make it fine, but we could miss this call if something bad
> happened. Finally, __ext4_get_inode_loc_noinmem() may probably get an
> empty inode buffer and trigger ext4 error.
> 
> For example, if we remove a nonexistent xattr on inode A,
> ext4_xattr_set_handle() will return ENODATA before invoking
> ext4_mark_iloc_dirty(), it will left an uptodate but zero buffer. We
> will get checksum error message in ext4_iget() when getting inode again.
> 
>   EXT4-fs error (device sda): ext4_lookup:1784: inode #131074: comm cat: iget: checksum invalid
> 
> Even worse, if we allocate another inode B at the same inode block, it
> will corrupt the inode A on disk when write back inode B.
> 
> So this patch initialize the inode buffer by filling the in-mem inode
> contents if we skip read I/O, ensure that the buffer is really uptodate.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/inode.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 3c36e701e30e..a8388ec91f9f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4441,12 +4441,12 @@ static int ext4_fill_raw_inode(struct inode *inode, struct ext4_inode *raw_inode
>  
>  /*
>   * ext4_get_inode_loc returns with an extra refcount against the inode's
> - * underlying buffer_head on success. If 'in_mem' is true, we have all
> - * data in memory that is needed to recreate the on-disk version of this
> - * inode.
> + * underlying buffer_head on success. If we pass 'inode' and it does not
> + * have in-inode xattr, we have all inode data in memory that is needed
> + * to recreate the on-disk version of this inode.
>   */
>  static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
> -				struct ext4_iloc *iloc, int in_mem,
> +				struct inode *inode, struct ext4_iloc *iloc,
>  				ext4_fsblk_t *ret_block)
>  {
>  	struct ext4_group_desc	*gdp;
> @@ -4486,7 +4486,7 @@ static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
>  	 * is the only valid inode in the block, we need not read the
>  	 * block.
>  	 */
> -	if (in_mem) {
> +	if (inode && !ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
>  		struct buffer_head *bitmap_bh;
>  		int i, start;
>  
> @@ -4514,8 +4514,13 @@ static int __ext4_get_inode_loc(struct super_block *sb, unsigned long ino,
>  		}
>  		brelse(bitmap_bh);
>  		if (i == start + inodes_per_block) {
> +			struct ext4_inode *raw_inode =
> +				(struct ext4_inode *) (bh->b_data + iloc->offset);
> +
>  			/* all other inodes are free, so skip I/O */
>  			memset(bh->b_data, 0, bh->b_size);
> +			if (!ext4_test_inode_state(inode, EXT4_STATE_NEW))
> +				ext4_fill_raw_inode(inode, raw_inode);
>  			set_buffer_uptodate(bh);
>  			unlock_buffer(bh);
>  			goto has_buffer;
> @@ -4576,7 +4581,7 @@ static int __ext4_get_inode_loc_noinmem(struct inode *inode,
>  	ext4_fsblk_t err_blk;
>  	int ret;
>  
> -	ret = __ext4_get_inode_loc(inode->i_sb, inode->i_ino, iloc, 0,
> +	ret = __ext4_get_inode_loc(inode->i_sb, inode->i_ino, NULL, iloc,
>  					&err_blk);
>  
>  	if (ret == -EIO)
> @@ -4591,9 +4596,8 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
>  	ext4_fsblk_t err_blk;
>  	int ret;
>  
> -	/* We have all inode data except xattrs in memory here. */
> -	ret = __ext4_get_inode_loc(inode->i_sb, inode->i_ino, iloc,
> -		!ext4_test_inode_state(inode, EXT4_STATE_XATTR), &err_blk);
> +	ret = __ext4_get_inode_loc(inode->i_sb, inode->i_ino, inode, iloc,
> +					&err_blk);
>  
>  	if (ret == -EIO)
>  		ext4_error_inode_block(inode, err_blk, EIO,
> @@ -4606,7 +4610,7 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
>  int ext4_get_fc_inode_loc(struct super_block *sb, unsigned long ino,
>  			  struct ext4_iloc *iloc)
>  {
> -	return __ext4_get_inode_loc(sb, ino, iloc, 0, NULL);
> +	return __ext4_get_inode_loc(sb, ino, NULL, iloc, NULL);
>  }
>  
>  static bool ext4_should_enable_dax(struct inode *inode)
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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