linux-kernel - Re: [PATCH] lockdep: lockdep_set_notrack

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Message-ID: <uvf4ilncakodvwmu6kbzs4lrxgeegtanhyhsk52xj7foil65jm@p54wibff6bgc>
Date: Sun, 30 Jun 2024 20:10:45 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Waiman Long <longman@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, 
	Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH] lockdep: lockdep_set_notrack_class()

On Sun, Jun 30, 2024 at 06:08:21PM GMT, Waiman Long wrote:
> On 6/30/24 01:10, Kent Overstreet wrote:
> > Add a new helper to disable lockdep tracking entirely for a given class.
> > 
> > This is needed for bcachefs, which takes too many btree node locks for
> > lockdep to track. Instead, we have a single lockdep_map for "btree_trans
> > has any btree nodes locked", which makes more since given that we have
> > centralized lock management and a cycle detector.
> 
> Could you explain a bit more what the current novalidate_class is lacking
> WRT to the bcachefs lock? Is it excessive performance overhead or some bogus
> lockdep warning?

novalidate just switches off checking of lock ordering, but the fact
that the locks are held is still tracked.

bcachefs takes more btree node locks than lockdep can track, so I'm
switching to a single lockdep map for "this btree_trans has any btree
nodes locked" instead.