linux-kernel - Re: [PATCH 1/2] lockdep: Don't disable interrupts on RT in disable_irq_nosync

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Message-ID: <20250212094917.1ca8cc13@gandalf.local.home>
Date: Wed, 12 Feb 2025 09:49:17 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: linux-rt-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, Peter
 Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, Will
 Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Waiman Long
 <longman@...hat.com>, Guenter Roeck <linux@...ck-us.net>, Clark Williams
 <clrkwllms@...nel.org>
Subject: Re: [PATCH 1/2] lockdep: Don't disable interrupts on RT in
 disable_irq_nosync_lockdep.*()

On Wed, 12 Feb 2025 11:36:18 +0100
Sebastian Andrzej Siewior <bigeasy@...utronix.de> wrote:

> disable_irq_nosync_lockdep() disables interrupts with lockdep enabled to
> avoid false positive reports by lockdep that a certain lock has not been
> acquired with disabled interrupts. The user of this macros expects that
> a lock can be acquried without disabling interrupts because the IRQ line
> triggering the interrupt is disabled.
> 
> This triggers a warning on PREEMPT_RT because after
> disable_irq_nosync_lockdep.*() the following spinlock_t now is acquired
> with disabled interrupts.
> 
> On PREEMPT_RT there is no difference between spin_lock() and
> spin_lock_irq() so avoiding disabling interrupts in this case works for
> the two remaining callers as of today.
> 
> Don't disable interrupts on PREEMPT_RT in disable_irq_nosync_lockdep.*().
> 
> Reported-by: Guenter Roeck <linux@...ck-us.net>
> Closes: https://lore.kernel.org/760e34f9-6034-40e0-82a5-ee9becd24438@roeck-us.net
> Fixes: e8106b941ceab ("[PATCH] lockdep: core, add enable/disable_irq_irqsave/irqrestore() APIs")
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---
>  include/linux/interrupt.h | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
> index 8cd9327e4e78d..a1b1be9bf73b2 100644
> --- a/include/linux/interrupt.h
> +++ b/include/linux/interrupt.h
> @@ -448,7 +448,7 @@ irq_calc_affinity_vectors(unsigned int minvec, unsigned int maxvec,
>  static inline void disable_irq_nosync_lockdep(unsigned int irq)
>  {
>  	disable_irq_nosync(irq);
> -#ifdef CONFIG_LOCKDEP
> +#if defined(CONFIG_LOCKDEP) && !defined(CONFIG_PREEMPT_RT)

Hmm, should you also add a:

Suggested-by: Steven Rostedt (Google) <rostedt@...dmis.org>

?

  https://lore.kernel.org/all/20250211182113.4875751a@gandalf.local.home/

    ;-)

-- Steve

>  	local_irq_disable();
>  #endif
>  }