Date: Fri, 5 Jan 2018 11:49:41 -0500
To: Matthew Wilcox <willy@infradead.org>
Cc: Theodore Ts'o <tytso@mit.edu>,
        Byungchul Park <byungchul.park@lge.com>,
        Byungchul Park <max.byungchul.park@gmail.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, david@fromorbit.com,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        oleg@redhat.com, kernel-team@lge.com, daniel@ffwll.ch
Subject: Re: About the try to remove cross-release feature entirely by Ingo
Message-ID: <20180105164941.GA4032@fieldses.org>
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From: bfields@fieldses.org (J. Bruce Fields)
Sender: linux-kernel-owner@vger.kernel.org

On Mon, Jan 01, 2018 at 02:18:55AM -0800, Matthew Wilcox wrote:
> On Sat, Dec 30, 2017 at 06:00:57PM -0500, Theodore Ts'o wrote:
> > On Sat, Dec 30, 2017 at 05:40:28PM -0500, Theodore Ts'o wrote:
> > > On Sat, Dec 30, 2017 at 12:44:17PM -0800, Matthew Wilcox wrote:
> > > > 
> > > > I'm not sure I agree with this part.  What if we add a new TCP lock class
> > > > for connections which are used for filesystems/network block devices/...?
> > > > Yes, it'll be up to each user to set the lockdep classification correctly,
> > > > but that's a relatively small number of places to add annotations,
> > > > and I don't see why it wouldn't work.
> > > 
> > > I was exagerrating a bit for effect, I admit.  (but only a bit).
> 
> I feel like there's been rather too much of that recently.  Can we stick
> to facts as far as possible, please?
> 
> > > It can probably be for all TCP connections that are used by kernel
> > > code (as opposed to userspace-only TCP connections).  But it would
> > > probably have to be each and every device-mapper instance, each and
> > > every block device, each and every mounted file system, each and every
> > > bdi object, etc.
> > 
> > Clarification: all TCP connections that are used by kernel code would
> > need to be in their own separate lock class.  All TCP connections used
> > only by userspace could be in their own shared lock class.  You can't
> > use a one lock class for all kernel-used TCP connections, because of
> > the Network Block Device mounted on a local file system which is then
> > exported via NFS and squirted out yet another TCP connection problem.
> 
> So the false positive you're concerned about is write-comes-in-over-NFS
> (with socket lock held), NFS sends a write request to local filesystem,

I'm confused, what lock does Ted think the NFS server is holding over
NFS processing?

--b.