linux-ext4 - Re: [PATCH 2/5] ext4: do not convert the unwritten extents if data writeback fails

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Message-ID: <20241220102804.m2a4zkiypahqbuvz@quack3>
Date: Fri, 20 Dec 2024 11:28:04 +0100
From: Jan Kara <jack@...e.cz>
To: libaokun@...weicloud.com
Cc: linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca,
	jack@...e.cz, linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
	yangerkun@...wei.com, Baokun Li <libaokun1@...wei.com>
Subject: Re: [PATCH 2/5] ext4: do not convert the unwritten extents if data
 writeback fails

On Fri 20-12-24 14:07:54, libaokun@...weicloud.com wrote:
> From: Baokun Li <libaokun1@...wei.com>
> 
> When dioread_nolock is turned on (the default), it will convert unwritten
> extents to written at ext4_end_io_end(), even if the data writeback fails.
> 
> It leads to the possibility that stale data may be exposed when the
> physical block corresponding to the file data is read-only (i.e., writes
> return -EIO, but reads are normal).
> 
> Therefore a new ext4_io_end->flags EXT4_IO_END_FAILED is added, which
> indicates that some bio write-back failed in the current ext4_io_end.
> When this flag is set, the unwritten to written conversion is no longer
> performed. Users can read the data normally until the caches are dropped,
> after that, the failed extents can only be read to all 0.
> 
> Signed-off-by: Baokun Li <libaokun1@...wei.com>

Looks good. Feel free to add:

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

								Honza

> ---
>  fs/ext4/ext4.h    |  3 ++-
>  fs/ext4/page-io.c | 16 ++++++++++++++--
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 4e7de7eaa374..9da0e32af02a 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -278,7 +278,8 @@ struct ext4_system_blocks {
>  /*
>   * Flags for ext4_io_end->flags
>   */
> -#define	EXT4_IO_END_UNWRITTEN	0x0001
> +#define EXT4_IO_END_UNWRITTEN	0x0001
> +#define EXT4_IO_END_FAILED	0x0002
>  
>  struct ext4_io_end_vec {
>  	struct list_head list;		/* list of io_end_vec */
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index f53b018ea259..6054ec27fb48 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -181,14 +181,25 @@ static int ext4_end_io_end(ext4_io_end_t *io_end)
>  		   "list->prev 0x%p\n",
>  		   io_end, inode->i_ino, io_end->list.next, io_end->list.prev);
>  
> -	io_end->handle = NULL;	/* Following call will use up the handle */
> -	ret = ext4_convert_unwritten_io_end_vec(handle, io_end);
> +	/*
> +	 * Do not convert the unwritten extents if data writeback fails,
> +	 * or stale data may be exposed.
> +	 */
> +	io_end->handle = NULL;  /* Following call will use up the handle */
> +	if (unlikely(io_end->flag & EXT4_IO_END_FAILED)) {
> +		ret = -EIO;
> +		if (handle)
> +			jbd2_journal_free_reserved(handle);
> +	} else {
> +		ret = ext4_convert_unwritten_io_end_vec(handle, io_end);
> +	}
>  	if (ret < 0 && !ext4_forced_shutdown(inode->i_sb)) {
>  		ext4_msg(inode->i_sb, KERN_EMERG,
>  			 "failed to convert unwritten extents to written "
>  			 "extents -- potential data loss!  "
>  			 "(inode %lu, error %d)", inode->i_ino, ret);
>  	}
> +
>  	ext4_clear_io_unwritten_flag(io_end);
>  	ext4_release_io_end(io_end);
>  	return ret;
> @@ -339,6 +350,7 @@ static void ext4_end_bio(struct bio *bio)
>  			     bio->bi_status, inode->i_ino,
>  			     (unsigned long long)
>  			     bi_sector >> (inode->i_blkbits - 9));
> +		io_end->flag |= EXT4_IO_END_FAILED;
>  		mapping_set_error(inode->i_mapping,
>  				blk_status_to_errno(bio->bi_status));
>  	}
> -- 
> 2.46.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR