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

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Date:   Tue, 16 Aug 2022 09:43:16 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Christian Brauner <brauner@...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, 2022-08-16 at 15:33 +0200, Christian Brauner wrote:
> 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.
> 

We probably could, but setattr_copy has a lot of callers and most
filesystems don't need this.  Also, there are some cases where we don't
want to update the i_version after a setattr.

In particular, if you do a truncate and the size doesn't change, then
you really don't want to update the timestamps (and therefore the
i_version shouldn't change either).


> >  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
> > 

-- 
Jeff Layton <jlayton@...nel.org>