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

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Date:   Wed, 17 Aug 2022 09:28:52 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Jan Kara <jack@...e.cz>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Lukas Czerner <lczerner@...hat.com>,
        Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH] ext4: fix i_version handling in ext4

On Wed, 2022-08-17 at 15:25 +0200, Jan Kara wrote:
> On Wed 17-08-22 09:09:58, Jeff Layton wrote:
> > On Wed, 2022-08-17 at 15:04 +0200, Jan Kara wrote:
> > > On Tue 16-08-22 09:15:22, 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>
> > > 
> > > After some verification (which was not completely trivial e.g. for
> > > directories) I agree all cases should be covered. Feel free to add:
> > > 
> > > Reviewed-by: Jan Kara <jack@...e.cz>
> > > 
> > > 								Honza
> > > 
> > 
> > Thanks.
> > 
> > I think this covers the typical cases, but there are some places I
> > missed:
> > 
> > The setacl codepath, for one, and there are a number of places that set
> > the ctime explicitly for hole punching and the like.
> 
> Hum, why is setacl() not covered by your change to ext4_xattr_set_handle()?
> ext4_set_acl() ends up calling it... I have checked hole punching (whole
> ext4_fallocate()) and it seems to be incrementing iversion where needed.
> 

Oh, ok! I mostly noticed the places I was "missing" by inspection. It's
possible that I don't need those changes after all. If you think this
patch is sufficient, then I'll plan to just go with this one.

> > I'm planning to
> > send a v2 once I do a bit more testing. I'll hold off on adding your
> > Reviewed-by just yet, since the final patch may be quite a bit
> > different.
> 
> OK, thanks!
> 
> 								Honza
> 
> > 
> > 
> > > > ---
> > > >  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>

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