linux-kernel - Re: [PATCH] locking/mutex: Initialize mutex::magic even when LOCKDEP=n

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Message-ID: <20251128093606.GF3245006@noisy.programming.kicks-ass.net>
Date: Fri, 28 Nov 2025 10:36:06 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-next@...r.kernel.org,
	akpm@...ux-foundation.org, Stephen Rothwell <sfr@...b.auug.org.au>,
	Nathan Chancellor <nathan@...nel.org>,
	Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] locking/mutex: Initialize mutex::magic even when
 LOCKDEP=n

On Tue, Nov 25, 2025 at 06:54:21AM -0800, Boqun Feng wrote:
> When DEBUG_MUTEXES=y and LOCKDEP=n, mutex_lock() still checks on
> ->magic, hence debug_mutex_init() should be called in
> mutex_init_generic() as well. While we are at it, decouple LOCKDEP
> logic from debug_mutex_init(), because in this way debug_mutex_init()
> only needs one parameter, and we now have mutex_init_lockep() for
> LOCKDEP=y scenarios.
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Closes: https://lore.kernel.org/lkml/20251117202214.4f710f02@canb.auug.org.au/
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Closes: https://lore.kernel.org/lkml/20251121215819.GA1374726@ax162/
> Fixes: 3572e2edc7b6 ("locking/mutex: Redo __mutex_init()")
> Reviewed-by: Waiman Long <longman@...hat.com>
> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> ---
> Peter,
> 
> Feel free to fold it into commit 3572e2edc7b6 ("locking/mutex: Redo
> __mutex_init()"), just resend it properly so it won't fall off your
> radar ;-)

Clearly I've been suffering too much mail again :/ Let me go frob stuff.