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From: Matthew Wilcox <willy@infradead.org>
To: Andreas Gruenbacher <agruenba@redhat.com>
Cc: "Andreas Grünbacher" <andreas.gruenbacher@gmail.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	"Junxiao Bi" <junxiao.bi@oracle.com>,
	"William Kucharski" <william.kucharski@oracle.com>,
	"Joseph Qi" <joseph.qi@linux.alibaba.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-f2fs-devel@lists.sourceforge.net,
	cluster-devel <cluster-devel@redhat.com>,
	Linux-MM <linux-mm@kvack.org>,
	ocfs2-devel@oss.oracle.com,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	linux-erofs@lists.ozlabs.org, "Christoph Hellwig" <hch@lst.de>,
	linux-btrfs@vger.kernel.org,
	"Steven Whitehouse" <swhiteho@redhat.com>,
	"Bob Peterson" <rpeterso@redhat.com>
Subject: Re: [Cluster-devel] [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead
Date: Thu, 18 Jun 2020 08:03:09 -0700
Message-ID: <20200618150309.GP8681@bombadil.infradead.org> (raw)
In-Reply-To: <CAHc6FU7NLRHKRJJ6c2kQT0ig8ed1n+3qR-YcSCWzXOeJCUsLbA@mail.gmail.com>

On Thu, Jun 18, 2020 at 02:46:03PM +0200, Andreas Gruenbacher wrote:
> On Wed, Jun 17, 2020 at 4:22 AM Matthew Wilcox <willy@infradead.org> wrote:
> > On Wed, Jun 17, 2020 at 02:57:14AM +0200, Andreas Grünbacher wrote:
> > > 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.
> 
> 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.

What I'm saying is that gfs2_fault should just be:

+static vm_fault_t gfs2_fault(struct vm_fault *vmf)
+{
+	struct inode *inode = file_inode(vmf->vma->vm_file);
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_holder gh;
+	vm_fault_t ret;
+	int err;
+
+	gfs2_holder_init(ip->i_gl, LM_ST_SHARED, 0, &gh);
+	err = gfs2_glock_nq(&gh);
+	if (err) {
+		ret = block_page_mkwrite_return(err);
+		goto out_uninit;
+	}
+	ret = filemap_fault(vmf);
+	gfs2_glock_dq(&gh);
+out_uninit:
+	gfs2_holder_uninit(&gh);
+	return ret;
+}

because by the time gfs2_fault() is called, map_pages() has already been
called and has failed to insert the necessary page, so we should just
acquire the glock now instead of trying again to look for the page in
the page cache.

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14 15:02 [PATCH v11 00/25] Change readahead API Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 01/25] mm: Move readahead prototypes from mm.h Matthew Wilcox
2020-04-15  9:10   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 02/25] mm: Return void from various readahead functions Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 03/25] mm: Ignore return value of ->readpages Matthew Wilcox
2020-04-15  9:17   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 04/25] mm: Move readahead nr_pages check into read_pages Matthew Wilcox
2020-04-15  9:19   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 05/25] mm: Add new readahead_control API Matthew Wilcox
2020-04-15  1:17   ` Andrew Morton
2020-04-15  2:18     ` Matthew Wilcox
2020-04-15  4:56       ` Andrew Morton
2020-04-15 11:22         ` Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 06/25] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-04-15  9:30   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 07/25] mm: Rename various 'offset' parameters to 'index' Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 08/25] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-04-15  9:31   ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 09/25] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 10/25] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 11/25] mm: Add readahead address space operation Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 12/25] mm: Move end_index check out of readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 13/25] mm: Add page_cache_readahead_unbounded Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 14/25] mm: Document why we don't set PageReadahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 15/25] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-06-16 22:36   ` [Cluster-devel] " Andreas Gruenbacher
2020-06-17  0:32     ` Matthew Wilcox
2020-06-17  0:57       ` Andreas Grünbacher
2020-06-17  2:21         ` Matthew Wilcox
2020-06-18 12:46           ` Andreas Gruenbacher
2020-06-18 15:03             ` Matthew Wilcox [this message]
2020-06-18 16:40               ` Andreas Gruenbacher
2020-04-14 15:02 ` [PATCH v11 17/25] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 18/25] erofs: Convert uncompressed files " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 19/25] erofs: Convert compressed " Matthew Wilcox
2020-04-21  5:42   ` Andrew Morton
2020-04-21  7:28     ` Gao Xiang
2020-04-14 15:02 ` [PATCH v11 20/25] ext4: Convert " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 21/25] ext4: Pass the inode to ext4_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 22/25] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 23/25] f2fs: Pass the inode to f2fs_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 24/25] fuse: Convert from readpages to readahead Matthew Wilcox
2020-04-20 11:14   ` Miklos Szeredi
2020-04-20 11:43     ` Matthew Wilcox
2020-04-20 11:54       ` Miklos Szeredi
2020-04-14 15:02 ` [PATCH v11 25/25] iomap: " Matthew Wilcox

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