Re: [PATCH] rtc: rtc-cmos: Fix event handler registration ordering issue

[Bjorn Helgaas]

On Wed, Oct 12, 2022 at 08:07:01PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> 
> Because acpi_install_fixed_event_handler() enables the event
> automatically on success, it is incorrect to call it before the
> handler routine passed to it is ready to handle events.
> 
> Unfortunately, the rtc-cmos driver does exactly the incorrect thing
> by calling cmos_wake_setup(), which passes rtc_handler() to
> acpi_install_fixed_event_handler(), before cmos_do_probe(), because
> rtc_handler() uses dev_get_drvdata() to get to the cmos object
> pointer and the driver data pointer is only populated in
> cmos_do_probe().
> 
> This leads to a NULL pointer dereference in rtc_handler() on boot
> if the RTC fixed event happens to be active at the init time.
> 
> To address this issue, change the initialization ordering of the
> driver so that cmos_wake_setup() is always called after a successful
> cmos_do_probe() call.
> 
> While at it, change cmos_pnp_probe() to call cmos_do_probe() after
> the initial if () statement used for computing the IRQ argument to
> be passed to cmos_do_probe() which is cleaner than calling it in
> each branch of that if () (local variable "irq" can be of type int,
> because it is passed to that function as an argument of type int).
> 
> Note that commit 6492fed7d8c9 ("rtc: rtc-cmos: Do not check
> ACPI_FADT_LOW_POWER_S0") caused this issue to affect a larger number
> of systems, because previously it only affected systems with
> ACPI_FADT_LOW_POWER_S0 set, but it is present regardless of that
> commit.
> 
> Fixes: 6492fed7d8c9 ("rtc: rtc-cmos: Do not check ACPI_FADT_LOW_POWER_S0")
> Fixes: a474aaedac99 ("rtc-cmos: move wake setup from ACPI glue into RTC driver")
> Link: https://lore.kernel.org/linux-acpi/20221010141630.zfzi7mk7zvnmclzy@xxxxxxxxxxxxxxxxxxx/
> Reported-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Reviewed-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

Yep, I blew it with a474aaedac99, sorry about that.

Possibly could call cmos_wake_setup() from cmos_do_probe() instead of
from cmos_pnp_probe() and cmos_platform_probe()?  Then there would be
a single call site and it would be closer to the actual dependency on
dev_set_drvdata().  Either way is fine with me.

Unrelated, but I happened to notice that pnp_irq() returns -1 for
failure, and this note suggests that possibly returning 0 would be
better:

  https://lore.kernel.org/r/CAHk-=wg2Pkb9kbfbstbB91AJA2SF6cySbsgHG-iQMq56j3VTcA@xxxxxxxxxxxxxx

> ---
>  drivers/rtc/rtc-cmos.c |   29 +++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)
> 
> Index: linux-pm/drivers/rtc/rtc-cmos.c
> ===================================================================
> --- linux-pm.orig/drivers/rtc/rtc-cmos.c
> +++ linux-pm/drivers/rtc/rtc-cmos.c
> @@ -1352,10 +1352,10 @@ static void cmos_check_acpi_rtc_status(s
>  
>  static int cmos_pnp_probe(struct pnp_dev *pnp, const struct pnp_device_id *id)
>  {
> -	cmos_wake_setup(&pnp->dev);
> +	int irq, ret;
>  
>  	if (pnp_port_start(pnp, 0) == 0x70 && !pnp_irq_valid(pnp, 0)) {
> -		unsigned int irq = 0;
> +		irq = 0;
>  #ifdef CONFIG_X86
>  		/* Some machines contain a PNP entry for the RTC, but
>  		 * don't define the IRQ. It should always be safe to
> @@ -1364,13 +1364,17 @@ static int cmos_pnp_probe(struct pnp_dev
>  		if (nr_legacy_irqs())
>  			irq = RTC_IRQ;
>  #endif
> -		return cmos_do_probe(&pnp->dev,
> -				pnp_get_resource(pnp, IORESOURCE_IO, 0), irq);
>  	} else {
> -		return cmos_do_probe(&pnp->dev,
> -				pnp_get_resource(pnp, IORESOURCE_IO, 0),
> -				pnp_irq(pnp, 0));
> +		irq = pnp_irq(pnp, 0);
>  	}
> +
> +	ret = cmos_do_probe(&pnp->dev, pnp_get_resource(pnp, IORESOURCE_IO, 0), irq);
> +	if (ret)
> +		return ret;
> +
> +	cmos_wake_setup(&pnp->dev);
> +
> +	return 0;
>  }
>  
>  static void cmos_pnp_remove(struct pnp_dev *pnp)
> @@ -1454,10 +1458,9 @@ static inline void cmos_of_init(struct p
>  static int __init cmos_platform_probe(struct platform_device *pdev)
>  {
>  	struct resource *resource;
> -	int irq;
> +	int irq, ret;
>  
>  	cmos_of_init(pdev);
> -	cmos_wake_setup(&pdev->dev);
>  
>  	if (RTC_IOMAPPED)
>  		resource = platform_get_resource(pdev, IORESOURCE_IO, 0);
> @@ -1467,7 +1470,13 @@ static int __init cmos_platform_probe(st
>  	if (irq < 0)
>  		irq = -1;
>  
> -	return cmos_do_probe(&pdev->dev, resource, irq);
> +	ret = cmos_do_probe(&pdev->dev, resource, irq);
> +	if (ret)
> +		return ret;
> +
> +	cmos_wake_setup(&pdev->dev);
> +
> +	return 0;
>  }
>  
>  static int cmos_platform_remove(struct platform_device *pdev)
> 
> 
>