linux-ext4 - Re: [PATCH 03/27] ext4: don't write back data before punch hole in nojournal mode

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Message-ID: <20241204112705.vb2vhlklnzswtvlf@quack3>
Date: Wed, 4 Dec 2024 12:27:05 +0100
From: Jan Kara <jack@...e.cz>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, tytso@....edu,
	adilger.kernel@...ger.ca, jack@...e.cz, ritesh.list@...il.com,
	hch@...radead.org, djwong@...nel.org, david@...morbit.com,
	zokeefe@...gle.com, yi.zhang@...wei.com, chengzhihao1@...wei.com,
	yukuai3@...wei.com, yangerkun@...wei.com
Subject: Re: [PATCH 03/27] ext4: don't write back data before punch hole in
 nojournal mode

On Tue 22-10-24 19:10:34, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> There is no need to write back all data before punching a hole in
> data=ordered|writeback mode since it will be dropped soon after removing
> space, so just remove the filemap_write_and_wait_range() in these modes.
> However, in data=journal mode, we need to write dirty pages out before
> discarding page cache in case of crash before committing the freeing
> data transaction, which could expose old, stale data.
> 
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

With the ext4_truncate_page_cache_block_range() function I propose, this
will get slightly simpler. But overall the patch looks good.

								Honza

> ---
>  fs/ext4/inode.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index f8796f7b0f94..94b923afcd9c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3965,17 +3965,6 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>  
>  	trace_ext4_punch_hole(inode, offset, length, 0);
>  
> -	/*
> -	 * Write out all dirty pages to avoid race conditions
> -	 * Then release them.
> -	 */
> -	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
> -		ret = filemap_write_and_wait_range(mapping, offset,
> -						   offset + length - 1);
> -		if (ret)
> -			return ret;
> -	}
> -
>  	inode_lock(inode);
>  
>  	/* No need to punch hole beyond i_size */
> @@ -4037,6 +4026,21 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>  		ret = ext4_update_disksize_before_punch(inode, offset, length);
>  		if (ret)
>  			goto out_dio;
> +
> +		/*
> +		 * For journalled data we need to write (and checkpoint) pages
> +		 * before discarding page cache to avoid inconsitent data on
> +		 * disk in case of crash before punching trans is committed.
> +		 */
> +		if (ext4_should_journal_data(inode)) {
> +			ret = filemap_write_and_wait_range(mapping,
> +					first_block_offset, last_block_offset);
> +			if (ret)
> +				goto out_dio;
> +		}
> +
> +		ext4_truncate_folios_range(inode, first_block_offset,
> +					   last_block_offset + 1);
>  		truncate_pagecache_range(inode, first_block_offset,
>  					 last_block_offset);
>  	}
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR