linux-kernel - Re: [PATCH 2/6] locking/lockdep: lockdep_set_no_check

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Message-ID: <20231124095804.GO3818@noisy.programming.kicks-ass.net>
Date:   Fri, 24 Nov 2023 10:58:04 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org,
        boqun.feng@...il.com, longman@...hat.com, will@...nel.org,
        mingo@...hat.com
Subject: Re: [PATCH 2/6] locking/lockdep: lockdep_set_no_check_recursion()

On Wed, Nov 22, 2023 at 06:51:09PM -0500, Kent Overstreet wrote:
> This adds a method to tell lockdep not to check lock ordering within a
> lock class - but to still check lock ordering w.r.t. other lock types.
> 
> This is for bcachefs, where for btree node locks we have our own
> deadlock avoidance strategy w.r.t. other btree node locks (cycle
> detection), but we still want lockdep to check lock ordering w.r.t.
> other lock types.

So earlier you added custom sort order.

Additionally there is the wound-wait mutexes that also have semantics
similar to what you describe.

Explain why you can't use either your own added feature or the existing
infrastructure to solve this?