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

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Message-ID: <2e997e85-fcf8-44bc-92bf-7d035c24abda@roeck-us.net>
Date: Wed, 12 Feb 2025 06:11:12 -0800
From: Guenter Roeck <linux@...ck-us.net>
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>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 1/2] lockdep: Don't disable interrupts on RT in
 disable_irq_nosync_lockdep.*()

On Wed, Feb 12, 2025 at 11:36:18AM +0100, Sebastian Andrzej Siewior 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>

Tested-by: Guenter Roeck <linux@...ck-us.net>