linux-kernel - usage of DEFINE_WAIT_OVERRIDE_MAP(LD_WAIT

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Message-ID: <20251020145310.GA9608@redhat.com>
Date: Mon, 20 Oct 2025 16:53:10 +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: usage of DEFINE_WAIT_OVERRIDE_MAP(LD_WAIT_SLEEP)

Hi Sebastian,

(change subject to not add more confusion)

On 08/11, Sebastian Andrzej Siewior wrote:
>
> On 2025-08-01 12:24:29 [+0200], Oleg Nesterov wrote:
> > s/LD_WAIT_SLEEP/LD_WAIT_CONFIG/ needs another discussion even if I am right,
> > sorry for the confusion.
>
> You are correct Oleg. I've been just verifying it and yes: LD_WAIT_SLEEP
> suppresses also mutex while the intention is to only suppress
> spinlock_t.
> We have four users in tree, based on quick check all four should use
> CONFIG, three of them do use SLEEP.

No ;)

I was going to send the patch which does s/SLEEP/CONFIG/, but this
would be wrong. printk_legacy_map can use LD_WAIT_CONFIG, but lets
look at debug_objects_fill_pool()

	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
		/*
		 * Annotate away the spinlock_t inside raw_spinlock_t warning
		 * by temporarily raising the wait-type to WAIT_SLEEP, matching
		 * the preemptible() condition above.
		 */
		static DEFINE_WAIT_OVERRIDE_MAP(fill_pool_map, LD_WAIT_SLEEP);
		lock_map_acquire_try(&fill_pool_map);
		fill_pool();
		lock_map_release(&fill_pool_map);
	}

If CONFIG_PREEMPT_RT=y and preemptible() is true, LD_WAIT_CONFIG won't work.
lockdep will complain if fill_pool() takes a spinlock_t, spinlock is
LD_WAIT_SLEEP on RT.

I guess debug_objects_fill_pool() actually needs something like

	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible()) {
		static DEFINE_WAIT_OVERRIDE_MAP(fill_pool_map, LD_WAIT_CONFIG);
		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
			lock_map_acquire_try(&fill_pool_map);

		fill_pool();

		if (!IS_ENABLED(CONFIG_PREEMPT_RT))
			lock_map_release(&fill_pool_map);
	}

but this is obviously too ugly. I am wondering if we can cleanup this logic
somehow...

Oleg.