linux-kernel - Re: [PATCH 1/2] fs: initialize inode->__i

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Message-ID: <20230908121015.k2xmkbiw7dljj24g@quack3>
Date:   Fri, 8 Sep 2023 14:10:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel test robot <oliver.sang@...el.com>
Subject: Re: [PATCH 1/2] fs: initialize inode->__i_ctime to the epoch

On Fri 08-09-23 07:41:45, Jeff Layton wrote:
> On Fri, 2023-09-08 at 12:42 +0200, Jan Kara wrote:
> > On Thu 07-09-23 12:33:47, Jeff Layton wrote:
> > > With the advent of multigrain timestamps, we use inode_set_ctime_current
> > > to set the ctime, which can skip updating if the existing ctime appears
> > > to be in the future. Because we don't initialize this field at
> > > allocation time, that could prevent the ctime from being initialized
> > > properly when the inode is instantiated.
> > > 
> > > Always initialize the ctime field to the epoch so that the filesystem
> > > can set the timestamps properly later.
> > > 
> > > Reported-by: kernel test robot <oliver.sang@...el.com>
> > > Closes: https://lore.kernel.org/oe-lkp/202309071017.a64aca5e-oliver.sang@intel.com
> > > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > 
> > Looks good but don't you need the same treatment to atime after your patch
> > 2/2?
> > 
> > 
> 
> I don't think so. Most filesystems are doing something along the lines
> of this when allocating a new inode:
> 
>     inode->i_atime = inode->i_mtime = inode_set_ctime_current(inode);
> 
> ...and I think they pretty much all have to initialize i_atime properly,
> since someone could stat the inode before an atime update occurs.

Ah, right. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> > > ---
> > >  fs/inode.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/fs/inode.c b/fs/inode.c
> > > index 35fd688168c5..54237f4242ff 100644
> > > --- a/fs/inode.c
> > > +++ b/fs/inode.c
> > > @@ -168,6 +168,8 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> > >  	inode->i_fop = &no_open_fops;
> > >  	inode->i_ino = 0;
> > >  	inode->__i_nlink = 1;
> > > +	inode->__i_ctime.tv_sec = 0;
> > > +	inode->__i_ctime.tv_nsec = 0;
> > >  	inode->i_opflags = 0;
> > >  	if (sb->s_xattr)
> > >  		inode->i_opflags |= IOP_XATTR;
> > > 
> > > -- 
> > > 2.41.0
> > > 
> 
> -- 
> Jeff Layton <jlayton@...nel.org>
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR