linux-kernel - Re: [tip: locking/core] locking/mutex: Document that mutex

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Message-ID: <20231201121808.GL3818@noisy.programming.kicks-ass.net>
Date:   Fri, 1 Dec 2023 13:18:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux-tip-commits@...r.kernel.org, Jann Horn <jannh@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, x86@...nel.org
Subject: Re: [tip: locking/core] locking/mutex: Document that mutex_unlock()
 is non-atomic

On Fri, Dec 01, 2023 at 10:44:09AM -0000, tip-bot2 for Jann Horn wrote:

> --- a/Documentation/locking/mutex-design.rst
> +++ b/Documentation/locking/mutex-design.rst
> @@ -101,6 +101,12 @@ features that make lock debugging easier and faster:
>      - Detects multi-task circular deadlocks and prints out all affected
>        locks and tasks (and only those tasks).
>  
> +Releasing a mutex is not an atomic operation: Once a mutex release operation

I still object to this confusing usage of atomic. Also all this also
applies to all sleeping locks, rwsem etc. I don't see why we need to
special case mutex here.

Also completion_done() has an explicit lock+unlock on wait.lock to
deal with this there.