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Date: Tue, 12 Dec 2017 07:39:16 -0800
From: Matthew Wilcox <willy@infradead.org>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Byungchul Park <byungchul.park@lge.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Subject: Re: [PATCH] locking/lockdep: Add CONFIG_LOCKDEP_AGGRESSIVE
Message-ID: <20171212153916.GA9570@bombadil.infradead.org>
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On Tue, Dec 12, 2017 at 08:03:43AM -0500, Theodore Ts'o wrote:
> On Tue, Dec 12, 2017 at 02:20:32PM +0900, Byungchul Park wrote:
> > The *problem* is false positives, since locks and waiters in
> > kernel are not classified properly, at the moment, which is just
> > a fact that is not related to cross-release stuff at all. IOW,
> > that would be useful once all locks and waiters are classified
> > correctly. It might take time but the classifying is a must-do
> > we have to keep doing.
> 
> This is the wrong attitude.  The reason why LOCKDEP was so powerful
> was because it automatically classified locks, instead of requiring
> developers to document the locking hierarchy.  Requiring developers to
> have to document and classified locks --- especially when the d*mned
> mechanisms for doign so are so primitive and not even documented ---
> is a complete non-strarter.

That's not fair.  We had to annotate i_mutex nesting, for example, and
several other places.  crosslock doesn't change anything in this respect,
it's just that the case that you hit every damn day as a filesystem
developer is something that the normal person almost never does.

> So are you willing to take my patch?  Or give me permission to keep in
> the ext4 tree?

He sent a patch earlier ...