linux-ext4 - Re: [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be marked dirty

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Message-Id: <20191023063557.21C964C050@d06av22.portsmouth.uk.ibm.com>
Date:   Wed, 23 Oct 2019 12:05:55 +0530
From:   Ritesh Harjani <riteshh@...ux.ibm.com>
To:     Matthew Bobrowski <mbobrowski@...browski.org>, tytso@....edu,
        jack@...e.cz, adilger.kernel@...ger.ca
Cc:     linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hch@...radead.org, david@...morbit.com, darrick.wong@...cle.com
Subject: Re: [PATCH v5 02/12] ext4: iomap that extends beyond EOF should be
 marked dirty



On 10/21/19 2:47 PM, Matthew Bobrowski wrote:
> This patch is effectively addressed what Dave Chinner had found and
> fixed within this commit: 8a23414ee345. Justification for needing this
> modification has been provided below:
Not sure if this is a valid commit id. I couldn't find it.


> 
> When doing a direct IO that spans the current EOF, and there are
> written blocks beyond EOF that extend beyond the current write, the
> only metadata update that needs to be done is a file size extension.
> 
> However, we don't mark such iomaps as IOMAP_F_DIRTY to indicate that
> there is IO completion metadata updates required, and hence we may
> fail to correctly sync file size extensions made in IO completion when
> O_DSYNC writes are being used and the hardware supports FUA.
> 
> Hence when setting IOMAP_F_DIRTY, we need to also take into account
> whether the iomap spans the current EOF. If it does, then we need to
> mark it dirty so that IO completion will call generic_write_sync() to
> flush the inode size update to stable storage correctly.
> 
> Signed-off-by: Matthew Bobrowski <mbobrowski@...browski.org>


Otherwise, this patch looks good to me. You may add:

Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>



> ---
>   fs/ext4/inode.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 158eea9a1944..0dd29ae5cc8c 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3412,8 +3412,14 @@ static void ext4_set_iomap(struct inode *inode, struct iomap *iomap,
>   {
>   	u8 blkbits = inode->i_blkbits;
>   
> +	/*
> +	 * Writes that span EOF might trigger an I/O size update on completion,
> +	 * so consider them to be dirty for the purposes of O_DSYNC, even if
> +	 * there is no other metadata changes being made or are pending here.
> +	 */
>   	iomap->flags = 0;
> -	if (ext4_inode_datasync_dirty(inode))
> +	if (ext4_inode_datasync_dirty(inode) ||
> +	    offset + length > i_size_read(inode))
>   		iomap->flags |= IOMAP_F_DIRTY;
>   
>   	if (map->m_flags & EXT4_MAP_NEW)
>