linux-kernel - Re: usage of DEFINE_WAIT_OVERRIDE_MAP(LD_WAIT

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Message-ID: <20251024102616.GD771@redhat.com>
Date: Fri, 24 Oct 2025 12:26:16 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: "Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>, Tejun Heo <tj@...nel.org>,
	David Vernet <dvernet@...a.com>, Barret Rhoden <brho@...gle.com>,
	Josh Don <joshdon@...gle.com>, Crystal Wood <crwood@...hat.com>,
	linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	Juri Lelli <juri.lelli@...hat.com>, Ben Segall <bsegall@...gle.com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wander Lairson Costa <wander@...hat.com>
Subject: Re: usage of DEFINE_WAIT_OVERRIDE_MAP(LD_WAIT_SLEEP)

On 10/23, Sebastian Andrzej Siewior wrote:
>
> On 2025-10-23 17:53:40 [+0200], Oleg Nesterov wrote:
> > Sebastian,
> Hi Oleg,
>
> > sorry. I guess this is my fault, but I can't understand your reply...
> > Could you spell please?
>
> So you refer to this:
> | /* PREEMPT_RT kernels map spinlock to rt_mutex */
> | #include <linux/rtmutex.h>
> |
> | typedef struct spinlock {
> | 	struct rt_mutex_base	lock;
> | #ifdef CONFIG_DEBUG_LOCK_ALLOC
> | 	struct lockdep_map	dep_map;
> | #endif
> | } spinlock_t;
>
> spinlock_t on PREEMPT_RT does not use (struct) rt_mutex as the comment
> claims. It uses just the basic building block which is "struct
> rt_mutex_base". This requires linux/rtmutex.h.
>
> spinlock_t on PREEMPT_RT uses LD_WAIT_CONFIG via SPIN_DEP_MAP_INIT as
> !PREEMPT_RT. Nothing changes here.

Ah, indeed, I was confused and didn't even bother to read the definitions
below, spinlock->dep_map is initialized by the same SPIN_DEP_MAP_INIT()...

Sebastian, thanks for correcting me! Sorry, I could not carefully read
your emails yesterday.

Oleg.