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Date: Thu, 18 Jun 2020 18:40:15 +0200 From: Andreas Gruenbacher <agruenba@...hat.com> To: Matthew Wilcox <willy@...radead.org> Cc: Andreas Grünbacher <andreas.gruenbacher@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, linux-xfs <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 Thu, Jun 18, 2020 at 5:03 PM Matthew Wilcox <willy@...radead.org> wrote: > > 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@...radead.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. Okay, that's great. Thanks, Andreas
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