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Date:   Thu, 13 Oct 2022 23:34:35 +0200
From:   Alexandre Belloni <alexandre.belloni@bootlin.com>
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Alessandro Zummo <a.zummo@towertech.it>,
        Mario Limonciello <mario.limonciello@amd.com>,
        linux-rtc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
        Linux ACPI <linux-acpi@vger.kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH] rtc: rtc-cmos: Fix event handler registration ordering
 issue
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References: <5629262.DvuYhMxLoT@kreacher>
 <20221012205757.GA3118709@bhelgaas>
 <CAJZ5v0gWG1qVzwSy19SSqFmxL7NZRf1pkLR_buPoyCcj4f0FLw@mail.gmail.com>
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On 13/10/2022 13:38:31+0200, Rafael J. Wysocki wrote:
> On Wed, Oct 12, 2022 at 11:00 PM Bjorn Helgaas <helgaas@kernel.org> wrote:
> >
> > On Wed, Oct 12, 2022 at 08:07:01PM +0200, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > >
> > > 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@techsingularity.net/
> > > Reported-by: Mel Gorman <mgorman@techsingularity.net>
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > Reviewed-by: Bjorn Helgaas <bhelgaas@google.com>
> >
> > 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()?
> 
> Sounds good.
> 
> I would prefer to send a separate patch for this on top of the
> $subject one, unless Alexandre wants me to do it all in one go.
> 
> Alexandre, what's your preference here?  Or would you prefer if I
> pushed this forward?
> 

I applied your patch, feel free to improve on top of that ;)

> > 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.
> 
> OK
> 
> > 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@mail.gmail.com
> 
> Probably.
> 
> In that case, though, it would be prudent to also explicitly discard
> IRQ resources where start is equal to 0.
> 
> >
> > > ---
> > >  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)
> > >
> > >
> > >

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com