linux-kernel - Re: [RFC RESEND v10 03/14] irq & spin_lock: Add counted interrupt disabling/enabling

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Message-ID: <20250617111157.36b1b17e@gandalf.local.home>
Date: Tue, 17 Jun 2025 11:11:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Lyude Paul <lyude@...hat.com>, rust-for-linux@...r.kernel.org, Thomas
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 Sander Mateos <csander@...estorage.com>, Ryo Takakura
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Subject: Re: [RFC RESEND v10 03/14] irq & spin_lock: Add counted interrupt
 disabling/enabling

On Tue, 17 Jun 2025 07:34:10 -0700
Boqun Feng <boqun.feng@...il.com> wrote:

> Because the new local_interrupt_{disable, enable}() participate the
> preempt count game as well, for example, __raw_spin_lock_irq_disable()
> doesn't call an additional preempt_disable() and
> __raw_spin_unlock_irq_enable() doesn't call preempt_enable(). And the
> following can happen:
> 
> 	spin_lock(a);
> 	// preemption is disabled.
> 	<interrupted and set need_resched>
> 
> 	spin_lock_irq_disable(b);
> 
> 	spin_unlock(a);
> 	spin_unlock_irq_enable(b):
> 	  local_interrupt_enable():
> 	  // need to check should_resched, otherwise preemption won't
> 	  // happen.

Ah, because preempt count can be set to non-zero *before* interrupts are
disabled. That makes sense. Thanks.

Hmm, I wonder if we should add a comment stating that here?

-- Steve