linux-kernel - Re: About the try to remove cross-release feature entirely by Ingo

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Date:   Sat, 30 Dec 2017 17:40:28 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Byungchul Park <byungchul.park@....com>,
        Byungchul Park <max.byungchul.park@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, david@...morbit.com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Amir Goldstein <amir73il@...il.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        oleg@...hat.com, kernel-team@....com, daniel@...ll.ch
Subject: Re: About the try to remove cross-release feature entirely by Ingo

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).

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.

The point I was trying to drive home is that "all we have to do is
just classify everything well or just invalidate the right lock
objects" is a massive understatement of the complexity level of what
would be required, or the number of locks/completion handlers that
would have to be blacklisted.

						- Ted