linux-ext4 - Re: [PATCH v3 1/3] ext4: don't increase iversion counter for ea

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Message-ID: <20220816115248.2xj25pcays7dkrpp@quack3>
Date:   Tue, 16 Aug 2022 13:52:48 +0200
From:   Jan Kara <jack@...e.cz>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Lukas Czerner <lczerner@...hat.com>, linux-ext4@...r.kernel.org,
        tytso@....edu, jack@...e.cz, linux-fsdevel@...r.kernel.org,
        ebiggers@...nel.org, david@...morbit.com
Subject: Re: [PATCH v3 1/3] ext4: don't increase iversion counter for
 ea_inodes

On Fri 12-08-22 14:42:36, Jeff Layton wrote:
> On Fri, 2022-08-12 at 14:37 +0200, Lukas Czerner wrote:
> > ea_inodes are using i_version for storing part of the reference count so
> > we really need to leave it alone.
> > 
> > The problem can be reproduced by xfstest ext4/026 when iversion is
> > enabled. Fix it by not calling inode_inc_iversion() for EXT4_EA_INODE_FL
> > inodes in ext4_mark_iloc_dirty().
> > 
> > Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> > Reviewed-by: Jan Kara <jack@...e.cz>
> > Reviewed-by: Jeff Layton <jlayton@...nel.org>
> > ---
> > v2, v3: no change
> > 
> >  fs/ext4/inode.c | 7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 601214453c3a..2a220be34caa 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -5731,7 +5731,12 @@ int ext4_mark_iloc_dirty(handle_t *handle,
> >  	}
> >  	ext4_fc_track_inode(handle, inode);
> >  
> > -	if (IS_I_VERSION(inode))
> > +	/*
> > +	 * ea_inodes are using i_version for storing reference count, don't
> > +	 * mess with it
> > +	 */
> > +	if (IS_I_VERSION(inode) &&
> > +	    !(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL))
> >  		inode_inc_iversion(inode);
> >  
> >  	/* the do_update_inode consumes one bh->b_count */
> 
> 
> I've spent some time writing tests for the i_version counter (still
> quite rough right now), and what I've found is that this particular
> inode_inc_iversion results in the counter being bumped on _reads_ as
> well as writes, due to the atime changing. This call to
> inode_inc_iversion seems to make no sense, as we aren't bumping the
> mtime here.
> 
> I'm still working on and testing this, but I think we'll probably just
> want to remove this inode_inc_iversion entirely, and leave the i_version
> bumping for normal files to happen when the timestamps are updated. So
> far, my testing seems to indicate that that does the right thing.

I agree that inode_inc_iversion() may be overly agressive here but where
else does get iversion updated for things like inode owner update or
permission changes?

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR