From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Gruenbacher Date: Thu, 18 Jun 2020 14:46:03 +0200 Subject: [Ocfs2-devel] [Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead In-Reply-To: <20200617022157.GF8681@bombadil.infradead.org> References: <20200414150233.24495-1-willy@infradead.org> <20200414150233.24495-17-willy@infradead.org> <20200617003216.GC8681@bombadil.infradead.org> <20200617022157.GF8681@bombadil.infradead.org> Message-ID: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Matthew Wilcox Cc: =?UTF-8?Q?Andreas_Gr=C3=BCnbacher?= , Andrew Morton , linux-xfs , Junxiao Bi , William Kucharski , Joseph Qi , John Hubbard , LKML , linux-f2fs-devel@lists.sourceforge.net, cluster-devel , Linux-MM , ocfs2-devel@oss.oracle.com, linux-fsdevel , linux-ext4 , linux-erofs@lists.ozlabs.org, Christoph Hellwig , linux-btrfs@vger.kernel.org, Steven Whitehouse , Bob Peterson On Wed, Jun 17, 2020 at 4:22 AM Matthew Wilcox 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 : > > > > > > 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 : > > > > > From: "Matthew Wilcox (Oracle)" > > > > > > > > > > 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