linux-ext4 - Re: [PATCH v4 06/12] ext4: using nofail preallocation in ext4_es_remove

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Date:   Wed, 3 May 2023 16:30:26 +0200
From:   Jan Kara <jack@...e.cz>
To:     Baokun Li <libaokun1@...wei.com>
Cc:     linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
        yangerkun@...wei.com, yukuai3@...wei.com
Subject: Re: [PATCH v4 06/12] ext4: using nofail preallocation in
 ext4_es_remove_extent()

On Mon 24-04-23 11:38:40, Baokun Li wrote:
> If __es_remove_extent() returns an error it means that when splitting
> extent, allocating an extent that must be kept failed, where returning
> an error directly would cause the extent tree to be inconsistent. So we
> use GFP_NOFAIL to pre-allocate an extent_status and pass it to
> __es_remove_extent() to avoid this problem.
> 
> In addition, since the allocated memory is outside the i_es_lock, the
> extent_status tree may change and the pre-allocated extent_status is
> no longer needed, so we release the pre-allocated extent_status when
> es->es_len is not initialized.
> 
> Suggested-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/extents_status.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
> index 7219116e0d68..f4d50cd501fc 100644
> --- a/fs/ext4/extents_status.c
> +++ b/fs/ext4/extents_status.c
> @@ -1458,6 +1458,7 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>  	ext4_lblk_t end;
>  	int err = 0;
>  	int reserved = 0;
> +	struct extent_status *es = NULL;
>  
>  	if (EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY)
>  		return 0;
> @@ -1472,17 +1473,25 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
>  	end = lblk + len - 1;
>  	BUG_ON(end < lblk);
>  
> +retry:
> +	if (err && !es)
> +		es = __es_alloc_extent(true);
>  	/*
>  	 * ext4_clear_inode() depends on us taking i_es_lock unconditionally
>  	 * so that we are sure __es_shrink() is done with the inode before it
>  	 * is reclaimed.
>  	 */
>  	write_lock(&EXT4_I(inode)->i_es_lock);
> -	err = __es_remove_extent(inode, lblk, end, &reserved, NULL);
> +	err = __es_remove_extent(inode, lblk, end, &reserved, es);
> +	if (es && !es->es_len)
> +		__es_free_extent(es);
>  	write_unlock(&EXT4_I(inode)->i_es_lock);
> +	if (err)
> +		goto retry;
> +
>  	ext4_es_print_tree(inode);
>  	ext4_da_release_space(inode, reserved);
> -	return err;
> +	return 0;
>  }
>  
>  static int __es_shrink(struct ext4_sb_info *sbi, int nr_to_scan,
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR