linux-kernel - Re: usage of DEFINE_WAIT_OVERRIDE_MAP(LD_WAIT

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Message-ID: <20251023192353.Wkng87fi@linutronix.de>
Date: Thu, 23 Oct 2025 21:23:53 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Oleg Nesterov <oleg@...hat.com>
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 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.

struct rt_mutex on the other hand uses LD_WAIT_SLEEP and this one is
like struct mutex but with PI.

Sebastian