Ocfs2 devel - Jun 2020 - [Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead

On Wed, Jun 17, 2020 at 02:57:14AM +0200, Andreas Gr?nbacher
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://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20191122235324.17245-1-agruenba
at
redhat.com/T/*t__;Iw!!GqivPVa7Brio!OyZYpIzgnFTc1rcoRozReSWo73Zx2STlBS2OMXGNUHASXwVPpRSW3M4uaNCCcJnxzw4Psw$
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.

On Wed, Jun 17, 2020 at 4:22 AM Matthew Wilcox <willy at infradead.org>
wrote:
> On Wed, Jun 17, 2020 at 02:57:14AM +0200, Andreas Gr?nbacher 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://urldefense.com/v3/__https://lore.kernel.org/linux-fsdevel/20191122235324.17245-1-agruenba
at
redhat.com/T/*t__;Iw!!GqivPVa7Brio!IekEw8uQR1N_S3Wqmk3aWZVcgHRjA1cp2KT7CkfJUM5xxPPXx_Jr5Is0-Z3rCNxzU5XYvQ$
>
> 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.
We'd still be grabbing a glock while holding a dependent page lock.
Another process could be holding the glock and could try to grab the
same page lock (i.e., a concurrent writer), leading to the same kind
of deadlock.

Andreas