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Date: Fri, 10 May 2024 07:53:52 +0200
From: Andrea Righi <andrea.righi@canonical.com>
To: David Howells <dhowells@redhat.com>
Cc: Jeff Layton <jlayton@kernel.org>, Steve French <smfrench@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Marc Dionne <marc.dionne@auristor.com>,
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	Dominique Martinet <asmadeus@codewreck.org>,
	Eric Van Hensbergen <ericvh@kernel.org>,
	Ilya Dryomov <idryomov@gmail.com>,
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	linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs@lists.linux.dev, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, Latchesar Ionkov <lucho@ionkov.net>,
	Christian Schoenebeck <linux_oss@crudebyte.com>
Subject: Re: [PATCH v5 40/40] 9p: Use netfslib read/write_iter
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On Thu, May 09, 2024 at 10:33:37PM +0100, David Howells wrote:
> Andrea Righi <andrea.righi@canonical.com> wrote:
> 
> > On Thu, Dec 21, 2023 at 01:23:35PM +0000, David Howells wrote:
> > > Use netfslib's read and write iteration helpers, allowing netfslib to take
> > > over the management of the page cache for 9p files and to manage local disk
> > > caching.  In particular, this eliminates write_begin, write_end, writepage
> > > and all mentions of struct page and struct folio from 9p.
> > > 
> > > Note that netfslib now offers the possibility of write-through caching if
> > > that is desirable for 9p: just set the NETFS_ICTX_WRITETHROUGH flag in
> > > v9inode->netfs.flags in v9fs_set_netfs_context().
> > > 
> > > Note also this is untested as I can't get ganesha.nfsd to correctly parse
> > > the config to turn on 9p support.
> > 
> > It looks like this patch has introduced a regression with autopkgtest,
> > see: https://bugs.launchpad.net/bugs/2056461
> > 
> > I haven't looked at the details yet, I just did some bisecting and
> > apparently reverting this one seems to fix the problem.
> > 
> > Let me know if you want me to test something in particular or if you
> > already have a potential fix. Otherwise I'll take a look.
> 
> Do you have a reproducer?
> 
> I'll be at LSF next week, so if I can't fix it tomorrow, I won't be able to
> poke at it until after that.
> 
> David

The only reproducer that I have at the moment is the autopkgtest command
mentioned in the bug, that is a bit convoluted, I'll try to see if I can
better isolate the problem and find a simpler reproducer, but I'll also
be travelling next week to a Canonical event.

At the moment I'll temporarily revert the commit (that seems to prevent
the issue from happening) and I'll keep you posted if I find something.

Thanks,
-Andrea