linux-kernel - Re: [for-next][PATCH 2/2] atomic64: Use arch_spin_locks instead of raw_spin

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Message-ID: <20250122143137.2f613629@gandalf.local.home>
Date: Wed, 22 Jan 2025 14:31:37 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, stable@...r.kernel.org, Thomas Gleixner
 <tglx@...utronix.de>, Linus Torvalds <torvalds@...ux-foundation.org>,
 Andreas Larsson <andreas@...sler.com>, Ludwig Rydberg
 <ludwig.rydberg@...sler.com>
Subject: Re: [for-next][PATCH 2/2] atomic64: Use arch_spin_locks instead of
 raw_spin_locks

On Wed, 22 Jan 2025 18:57:01 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> If I followed the maze right, then I get something like:
> 
> raw_spin_lock_irqsave(lock, flags)
>   local_irq_save(flags);
>   preempt_disable();
>   arch_spin_lock(lock);
>   mmiowb_spin_lock();
> 
> 
> And here you leave out that preempt_disable() and mmiowb stuff. The
> former is fine because local_irq_save() already makes things
> non-preemptible and there are no irq-state games. The mmiowb thing is
> fine because nothing inside this critical section cares about mmio.

Ah, yeah. OK, I don't plan on adding the preempt_disable() either as again,
this is really just an emulation of atomic64 for architectures that do not
support it.

I'll resend this with an updated change log.

Thanks for the review.

-- Steve