linux-kernel - Re: [PATCH 20/28] locking/lockdep: Refactorize check_noncircular and check

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Date:   Thu, 25 Apr 2019 21:48:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yuyang Du <duyuyang@...il.com>
Cc:     will.deacon@....com, mingo@...nel.org, bvanassche@....org,
        ming.lei@...hat.com, frederic@...nel.org, tglx@...utronix.de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/28] locking/lockdep: Refactorize check_noncircular and
 check_redundant

On Wed, Apr 24, 2019 at 06:19:26PM +0800, Yuyang Du wrote:
> These two functions now handle different check results themselves. A new
> check_path function is added to check whether there is a path in the
> dependency graph. No functional change.

This looks good, however I completely forgot we still had the redundant
thing.

It was added for cross-release (which has since been reverted) which
would generate a lot of redundant links (IIRC) but having it makes the
reports more convoluted -- basically, if we had an A-B-C relation, then
A-C will not be added to the graph because it is already covered. This
then means any report will include B, even though a shorter cycle might
have been possible.

Maybe we should make the whole redundant check depend on LOCKDEP_SMALL
for now.