linux-kernel - Re: [RFC PATCH 3/3][RESEND] xfs: mark the inode for high-res timestamp update in getattr

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Date:   Tue, 11 Apr 2023 11:58:34 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Chinner <david@...morbit.com>,
        Chuck Lever <chuck.lever@...cle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        linux-nfs@...r.kernel.org
Subject: Re: [RFC PATCH 3/3][RESEND] xfs: mark the inode for high-res
 timestamp update in getattr

On Tue, 2023-04-11 at 07:54 -0700, Darrick J. Wong wrote:
> On Tue, Apr 11, 2023 at 10:37:02AM -0400, Jeff Layton wrote:
> > When the mtime or ctime is being queried via getattr, ensure that we
> > mark the inode for a high-res timestamp update on the next pass. Also,
> > switch to current_cmtime for other c/mtime updates.
> > 
> > With this change, we're better off having the NFS server just ignore
> > the i_version field and have it use the ctime instead, so clear the
> > STATX_CHANGE_COOKIE flag in the result mask in ->getattr.
> > 
> > Signed-off-by: Jeff Layton <jlayton@...nel.org>
> > ---
> >  fs/xfs/libxfs/xfs_trans_inode.c |  2 +-
> >  fs/xfs/xfs_acl.c                |  2 +-
> >  fs/xfs/xfs_inode.c              |  2 +-
> >  fs/xfs/xfs_iops.c               | 15 ++++++++++++---
> >  4 files changed, 15 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_trans_inode.c b/fs/xfs/libxfs/xfs_trans_inode.c
> > index 8b5547073379..9ad7c229c617 100644
> > --- a/fs/xfs/libxfs/xfs_trans_inode.c
> > +++ b/fs/xfs/libxfs/xfs_trans_inode.c
> > @@ -63,7 +63,7 @@ xfs_trans_ichgtime(
> >  	ASSERT(tp);
> >  	ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
> >  
> > -	tv = current_time(inode);
> > +	tv = current_cmtime(inode);
> >  
> >  	if (flags & XFS_ICHGTIME_MOD)
> >  		inode->i_mtime = tv;
> > diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
> > index 791db7d9c849..461adc58cf8c 100644
> > --- a/fs/xfs/xfs_acl.c
> > +++ b/fs/xfs/xfs_acl.c
> > @@ -233,7 +233,7 @@ xfs_acl_set_mode(
> >  	xfs_ilock(ip, XFS_ILOCK_EXCL);
> >  	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
> >  	inode->i_mode = mode;
> > -	inode->i_ctime = current_time(inode);
> > +	inode->i_ctime = current_cmtime(inode);
> 
> Hmm, now we're adding a spinlock to all these updates.
> Does lockdep have anything exciting to say about this?
> 
> (I don't think it will, just wondering aloud...)
> 

I haven't seen anything, but I haven't done any extensive testing yet
either. Still, that might be a good reason to avoid locking in this
scheme if we can.

> >  	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
> >  
> >  	if (xfs_has_wsync(mp))
> > diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> > index 5808abab786c..80f9d731e261 100644
> > --- a/fs/xfs/xfs_inode.c
> > +++ b/fs/xfs/xfs_inode.c
> > @@ -843,7 +843,7 @@ xfs_init_new_inode(
> >  	ip->i_df.if_nextents = 0;
> >  	ASSERT(ip->i_nblocks == 0);
> >  
> > -	tv = current_time(inode);
> > +	tv = current_cmtime(inode);
> >  	inode->i_mtime = tv;
> >  	inode->i_atime = tv;
> >  	inode->i_ctime = tv;
> > diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> > index 24718adb3c16..a0b07f90e16c 100644
> > --- a/fs/xfs/xfs_iops.c
> > +++ b/fs/xfs/xfs_iops.c
> > @@ -565,6 +565,15 @@ xfs_vn_getattr(
> >  	if (xfs_is_shutdown(mp))
> >  		return -EIO;
> >  
> > +	/*
> > +	 * XFS uses the i_version infrastructure to track any change to
> > +	 * the inode, including atime updates. This means that the i_version
> > +	 * returned by getattr doesn't conform to what the callers expect.
> > +	 * Clear it here so that nfsd will fake up a change cookie from the
> > +	 * ctime instead.
> > +	 */
> > +	stat->result_mask &= ~STATX_CHANGE_COOKIE;
> > +
> >  	stat->size = XFS_ISIZE(ip);
> >  	stat->dev = inode->i_sb->s_dev;
> >  	stat->mode = inode->i_mode;
> > @@ -573,8 +582,8 @@ xfs_vn_getattr(
> >  	stat->gid = vfsgid_into_kgid(vfsgid);
> >  	stat->ino = ip->i_ino;
> >  	stat->atime = inode->i_atime;
> > -	stat->mtime = inode->i_mtime;
> > -	stat->ctime = inode->i_ctime;
> > +	if (request_mask & (STATX_CTIME|STATX_MTIME))
> > +		fill_cmtime_and_mark(inode, stat);
> 
> Should we be setting STATX_[CM]TIME in the result_mask, just in case the
> caller asked for ctime and not mtime?
> 
> 

We already set the result_mask in vfs_getattr_nosec:

    stat->result_mask |= STATX_BASIC_STATS;

...and it's OK to return more attrs than were requested.

The bigger issue here is that it's not setting the ctime and mtime
fields while leaving the STATX_CTIME and STATX_MTIME flags set. I'll
plan to fix that up in some fashion in the next post.

Thanks!

> >  	stat->blocks = XFS_FSB_TO_BB(mp, ip->i_nblocks + ip->i_delayed_blks);
> >  
> >  	if (xfs_has_v3inodes(mp)) {
> > @@ -917,7 +926,7 @@ xfs_setattr_size(
> >  	if (newsize != oldsize &&
> >  	    !(iattr->ia_valid & (ATTR_CTIME | ATTR_MTIME))) {
> >  		iattr->ia_ctime = iattr->ia_mtime =
> > -			current_time(inode);
> > +			current_cmtime(inode);
> >  		iattr->ia_valid |= ATTR_CTIME | ATTR_MTIME;
> >  	}
> >  
> > -- 
> > 2.39.2
> > 

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