linux-ext4 - Re: [PATCH] ext4: reject mount options not supported when remounting in handle_mount

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Date:   Wed, 22 Apr 2020 18:10:29 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com, stable@...nel.org,
        syzbot+bca9799bf129256190da@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: reject mount options not supported when remounting
 in handle_mount_opt()

On Wed 15-04-20 22:23:52, Ira Weiny wrote:
> On Wed, Apr 15, 2020 at 06:07:52PM -0400, Theodore Y. Ts'o wrote:
> > On Wed, Apr 15, 2020 at 01:25:37PM -0700, Ira Weiny wrote:
> > > This fundamentally changes the behavior from forcing the dax mode to be the
> > > same across the remount to only failing if we are going from non-dax to dax,
> > > adding -o dax on the remount?
> > > 
> > > But going from -o dax to 'not -o dax' would be ok?
> > > 
> > > FWIW after thinking about it some I _think_ it would be ok to allow the dax
> > > mode to change on a remount and let the inodes in memory stay in the mode they
> > > are at.  And newly loaded inodes would get the new mode...  Unfortunately
> > > without the STATX patch I have proposed the user does not have any way of
> > > knowing which files are in which mode.
> > 
> > We don't currently support mount -o nodax.
> 
> But we do support not supplying the option which means 'nodax' right?

Yeah, I second what Ira wrote. The new code does not seem to properly
detect a case when enabled mount option is removed for remount and thus the
feature would get disabled during remount as a result...

								Honza

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