linux-ext4 - Re: [PATCH 08/14] xfs: Convert to use invalidate

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Date:   Tue, 8 Jun 2021 14:23:40 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>, ceph-devel@...r.kernel.org,
        Chao Yu <yuchao0@...wei.com>,
        Damien Le Moal <damien.lemoal@....com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Jeff Layton <jlayton@...nel.org>,
        Johannes Thumshirn <jth@...nel.org>,
        linux-cifs@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-mm@...ck.org,
        linux-xfs@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
        Steve French <sfrench@...ba.org>, Ted Tso <tytso@....edu>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 08/14] xfs: Convert to use invalidate_lock

On Mon 07-06-21 08:56:33, Darrick J. Wong wrote:
> On Mon, Jun 07, 2021 at 04:52:18PM +0200, Jan Kara wrote:
> > Use invalidate_lock instead of XFS internal i_mmap_lock. The intended
> > purpose of invalidate_lock is exactly the same. Note that the locking in
> > __xfs_filemap_fault() slightly changes as filemap_fault() already takes
> > invalidate_lock.
> > 
> > Reviewed-by: Christoph Hellwig <hch@....de>
> > CC: <linux-xfs@...r.kernel.org>
> > CC: "Darrick J. Wong" <djwong@...nel.org>
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > ---
> >  fs/xfs/xfs_file.c  | 13 +++++++-----
> >  fs/xfs/xfs_inode.c | 50 ++++++++++++++++++++++++----------------------
> >  fs/xfs/xfs_inode.h |  1 -
> >  fs/xfs/xfs_super.c |  2 --
> >  4 files changed, 34 insertions(+), 32 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 396ef36dcd0a..7cb7703c2209 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -1282,7 +1282,7 @@ xfs_file_llseek(
> >   *
> >   * mmap_lock (MM)
> >   *   sb_start_pagefault(vfs, freeze)
> > - *     i_mmaplock (XFS - truncate serialisation)
> > + *     invalidate_lock (vfs/XFS_MMAPLOCK - truncate serialisation)
> >   *       page_lock (MM)
> >   *         i_lock (XFS - extent map serialisation)
> >   */
> > @@ -1303,24 +1303,27 @@ __xfs_filemap_fault(
> >  		file_update_time(vmf->vma->vm_file);
> >  	}
> >  
> > -	xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> >  	if (IS_DAX(inode)) {
> >  		pfn_t pfn;
> >  
> > +		xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> >  		ret = dax_iomap_fault(vmf, pe_size, &pfn, NULL,
> >  				(write_fault && !vmf->cow_page) ?
> >  				 &xfs_direct_write_iomap_ops :
> >  				 &xfs_read_iomap_ops);
> >  		if (ret & VM_FAULT_NEEDDSYNC)
> >  			ret = dax_finish_sync_fault(vmf, pe_size, pfn);
> > +		xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
> 
> I've been wondering if iomap_page_mkwrite and dax_iomap_fault should be
> taking these locks?  I guess that would violate the premise that iomap
> requires that callers arrange for concurrency control (i.e. iomap
> doesn't take locks).

Well, iomap does take page locks but I agree that generally it stays away
from high-level locks. So keeping invalidate_lock out of it makes more
sense to me as well.

> Code changes look fine, though.
> 
> Reviewed-by: Darrick J. Wong <djwong@...nel.org>

Thanks!

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