linux-kernel - Re: [PATCH] counter: interrupt-cnt: Protect enable/disable OPs with mutex

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Message-ID: <aBSxgDuw42kPlweT@pengutronix.de>
Date: Fri, 2 May 2025 13:50:24 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: William Breathitt Gray <wbg@...nel.org>
Cc: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] counter: interrupt-cnt: Protect enable/disable OPs with
 mutex

On Fri, May 02, 2025 at 08:43:18PM +0900, William Breathitt Gray wrote:
> On Fri, May 02, 2025 at 09:24:20AM +0000, Sverdlin, Alexander wrote:
> > Dear maintainers,
> > 
> > On Mon, 2025-03-31 at 18:36 +0200, A. Sverdlin wrote:
> > > From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > >
> > > Enable/disable seems to be racy on SMP, consider the following scenario:
> > >
> > > CPU0					CPU1
> > >
> > > interrupt_cnt_enable_write(true)
> > > {
> > > 	if (priv->enabled == enable)
> > > 		return 0;
> > >
> > > 	if (enable) {
> > > 		priv->enabled = true;
> > > 					interrupt_cnt_enable_write(false)
> > > 					{
> > > 						if (priv->enabled == enable)
> > > 							return 0;
> > >
> > > 						if (enable) {
> > > 							priv->enabled = true;
> > > 							enable_irq(priv->irq);
> > > 						} else {
> > > 							disable_irq(priv->irq)
> > > 							priv->enabled = false;
> > > 						}
> > > 		enable_irq(priv->irq);
> > > 	} else {
> > > 		disable_irq(priv->irq);
> > > 		priv->enabled = false;
> > > 	}
> > >
> > > The above would result in priv->enabled == false, but IRQ left enabled.
> > > Protect both write (above race) and read (to propagate the value on SMP)
> > > callbacks with a mutex.
> > >
> > > Signed-off-by: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > 
> > I've noticed that the patch has been marked as "Changes Requested" in
> > the patchwork, could it be a mistake? Because I never received any
> > change request.
> 
> Hi Alexander,
> 
> I can't comment on the patchwork status because I don't use that
> service, but I apologize nonetheless for the delay in responding to your
> patch submission. I'm hoping for an Ack from Oleksij, but this is a
> pretty straight-forward fix that I'll be happy to pick it up regardless.
> 
> Would you provide a Fixes line so the stable trees can pick this up for
> the necessary kernel versions?

Sorry for delay, you can add my
Acked-by: Oleksij Rempel <o.rempel@...gutronix.de>

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