linux-kernel - Re: [Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to mpage

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Date:   Tue, 16 Jun 2020 17:32:16 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-xfs@...r.kernel.org, Junxiao Bi <junxiao.bi@...cle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        John Hubbard <jhubbard@...dia.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-f2fs-devel@...ts.sourceforge.net,
        cluster-devel <cluster-devel@...hat.com>,
        Linux-MM <linux-mm@...ck.org>, ocfs2-devel@....oracle.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        linux-erofs@...ts.ozlabs.org, Christoph Hellwig <hch@....de>,
        linux-btrfs@...r.kernel.org,
        Steven Whitehouse <swhiteho@...hat.com>,
        Bob Peterson <rpeterso@...hat.com>
Subject: Re: [Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to
 mpage_readahead

On Wed, Jun 17, 2020 at 12:36:13AM +0200, Andreas Gruenbacher wrote:
> Am Mi., 15. Apr. 2020 um 23:39 Uhr schrieb Matthew Wilcox <willy@...radead.org>:
> > From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> >
> > Implement the new readahead aop and convert all callers (block_dev,
> > exfat, ext2, fat, gfs2, hpfs, isofs, jfs, nilfs2, ocfs2, omfs, qnx6,
> > reiserfs & udf).  The callers are all trivial except for GFS2 & OCFS2.
> 
> This patch leads to an ABBA deadlock in xfstest generic/095 on gfs2.
> 
> Our lock hierarchy is such that the inode cluster lock ("inode glock")
> for an inode needs to be taken before any page locks in that inode's
> address space.

How does that work for ...

writepage:              yes, unlocks (see below)
readpage:               yes, unlocks
invalidatepage:         yes
releasepage:            yes
freepage:               yes
isolate_page:           yes
migratepage:            yes (both)
putback_page:           yes
launder_page:           yes
is_partially_uptodate:  yes
error_remove_page:      yes

Is there a reason that you don't take the glock in the higher level
ops which are called before readhead gets called?  I'm looking at XFS,
and it takes the xfs_ilock SHARED in xfs_file_buffered_aio_read()
(called from xfs_file_read_iter).

Not that after -rc1 is a great time to be upending the locking model in
a filesystem ... but then, this has been baking in -mm for ten weeks and
the GFS2 mailing list has been on the cc for the patches for five months,
so I don't have a lot of sympathy for this.