[Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead

[Matthew Wilcox]

On Wed, Jun 17, 2020 at 02:57:14AM +0200, Andreas Grünbacher wrote:
> Am Mi., 17. Juni 2020 um 02:33 Uhr schrieb Matthew Wilcox <willy at infradead.org>:
> >
> > 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 at infradead.org>:
> > > > From: "Matthew Wilcox (Oracle)" <willy at infradead.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).
> 
> Right, the approach from the following thread might fix this:
> 
> https://lore.kernel.org/linux-fsdevel/20191122235324.17245-1-agruenba@redhat.com/T/#t

In general, I think this is a sound approach.

Specifically, I think FAULT_FLAG_CACHED can go away.  map_pages()
will bring in the pages which are in the page cache, so when we get to
gfs2_fault(), we know there's a reason to acquire the glock.