linux-ext4 - Re: [PATCH] ext4: fix i_version handling in ext4

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Message-ID: <20220816133340.mtaa7mxmgvhzffoh@wittgenstein>
Date:   Tue, 16 Aug 2022 15:33:40 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Lukas Czerner <lczerner@...hat.com>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] ext4: fix i_version handling in ext4

On Tue, Aug 16, 2022 at 09:15:22AM -0400, Jeff Layton wrote:
> ext4 currently updates the i_version counter when the atime is updated
> during a read. This is less than ideal as it can cause unnecessary cache
> invalidations with NFSv4. The increment in ext4_mark_iloc_dirty is also
> problematic since it can also corrupt the i_version counter for
> ea_inodes.
> 
> We aren't bumping the file times in ext4_mark_iloc_dirty, so changing
> the i_version there seems wrong, and is the cause of both problems.
> Remove that callsite and add increments to the setattr and setxattr
> codepaths (at the same time that we update the ctime). The i_version
> bump that already happens during timestamp updates should take care of
> the rest.
> 
> Cc: Lukas Czerner <lczerner@...hat.com>
> Cc: Jan Kara <jack@...e.cz>
> Cc: Christian Brauner <brauner@...nel.org>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---

Seems good to me. But it seems that the xfs patch you sent does have
inode_inc_version() right after setattr_copy() as well. So I wonder if
we couldn't just try and move inode_inc_version() into setattr_copy()
itself.

>  fs/ext4/inode.c | 10 +++++-----
>  fs/ext4/xattr.c |  2 ++
>  2 files changed, 7 insertions(+), 5 deletions(-)
> 
> I think this patch should probably supersede Lukas' patch entitled:
> 
>     ext4: don't increase iversion counter for ea_inodes
> 
> This will also mean that we'll need to respin the patch to turn on the
> i_version counter unconditionally in ext4 (though that should be
> trivial).
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 601214453c3a..a70921df89a5 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5342,6 +5342,7 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  	int error, rc = 0;
>  	int orphan = 0;
>  	const unsigned int ia_valid = attr->ia_valid;
> +	bool inc_ivers = IS_IVERSION(inode);
>  
>  	if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
>  		return -EIO;
> @@ -5425,8 +5426,8 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  			return -EINVAL;
>  		}
>  
> -		if (IS_I_VERSION(inode) && attr->ia_size != inode->i_size)
> -			inode_inc_iversion(inode);
> +		if (attr->ia_size == inode->i_size)
> +			inc_ivers = false;
>  
>  		if (shrink) {
>  			if (ext4_should_order_data(inode)) {
> @@ -5528,6 +5529,8 @@ int ext4_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>  	}
>  
>  	if (!error) {
> +		if (inc_ivers)
> +			inode_inc_iversion(inode);
>  		setattr_copy(mnt_userns, inode, attr);
>  		mark_inode_dirty(inode);
>  	}
> @@ -5731,9 +5734,6 @@ int ext4_mark_iloc_dirty(handle_t *handle,
>  	}
>  	ext4_fc_track_inode(handle, inode);
>  
> -	if (IS_I_VERSION(inode))
> -		inode_inc_iversion(inode);
> -
>  	/* the do_update_inode consumes one bh->b_count */
>  	get_bh(iloc->bh);
>  
> diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> index 533216e80fa2..4d84919d1c9c 100644
> --- a/fs/ext4/xattr.c
> +++ b/fs/ext4/xattr.c
> @@ -2412,6 +2412,8 @@ ext4_xattr_set_handle(handle_t *handle, struct inode *inode, int name_index,
>  	if (!error) {
>  		ext4_xattr_update_super_block(handle, inode->i_sb);
>  		inode->i_ctime = current_time(inode);
> +		if (IS_IVERSION(inode))
> +			inode_inc_iversion(inode);
>  		if (!value)
>  			no_expand = 0;
>  		error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
> -- 
> 2.37.2
>