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Date: Fri, 5 Jun 2015 05:35:43 +0300
From: Roger Quadros <rogerq@ti.com>
To: Grygorii Strashko <grygorii.strashko@ti.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Alexandre Courbot <gnurou@gmail.com>
CC: Geert Uytterhoeven <geert@linux-m68k.org>,
        "Grygorii.Strashko@linaro.org" <grygorii.strashko@linaro.org>,
        "Thomas Gleixner" <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
        "linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: Calling irq_set_irq_wake() from .set_irq_wake()?
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Hi,

On Wed, 3 Jun 2015 22:52:47 +0300
Grygorii Strashko <grygorii.strashko@ti.com> wrote:

> Hi Geert,
> 
> On 05/19/2015 12:38 PM, Geert Uytterhoeven wrote:
> > On Mon, May 18, 2015 at 4:52 PM, Grygorii.Strashko@linaro.org
> > <grygorii.strashko@linaro.org> wrote:
> >> On 05/18/2015 05:31 PM, Thomas Gleixner wrote:
> >>> On Sun, 17 May 2015, Geert Uytterhoeven wrote:
> >>>>>>> At least the recursive locking message no longer appears after the revert.
> >>>>>>>
> >>>>>>> [   30.591905] PM: Syncing filesystems ... done.
> >>>>>>> [   30.623060] Freezing user space processes ... (elapsed 0.003 seconds) done.
> >>>>>>> [   30.634470] Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
> >>>>>>> [   30.658288] sd 0:0:0:0: [sda] Synchronizing SCSI cache
> >>>>>>> [   30.663678]
> >>>>>>> [   30.663681] =============================================
> >>>>>>> [   30.663683] [ INFO: possible recursive locking detected ]
> >>>>>>> [   30.663688] 4.1.0-rc3 #1115 Not tainted
> >>>>>>> [   30.663693] ---------------------------------------------
> >>>>>>> [   30.663697] suspend.sh/2319 is trying to acquire lock:
> >>>>>>> [   30.663719]  (class){......}, at: [<c0096ebc>] __irq_get_desc_lock+0x48/0x88
> >>>>>>> [   30.663722]
> >>>>>>> [   30.663722] but task is already holding lock:
> >>>>>>> [   30.663734]  (class){......}, at: [<c0096ebc>] __irq_get_desc_lock+0x48/0x88
> >>>>>>
> >>>>>> Does this mean .set_irq_wake() cannot call irq_set_irq_wake()?
> >>>
> >>> It can call it, if it's guaranteed that this wont deadlock.
> >>>
> >>> To tell lockdep that you sure about that, you need to set a different
> >>> lock class for the child interrupts. irq_set_lockdep_class() is what
> >>> you want to use here.
> >>
> >> Hm. Seems we already have corresponding call in gpiochip_irq_map:
> >>
> >>   static int gpiochip_irq_map(struct irq_domain *d, unsigned int irq,
> >>                              irq_hw_number_t hwirq)
> >> {
> >>          struct gpio_chip *chip = d->host_data;
> >>
> >>          irq_set_chip_data(irq, chip);
> >>          irq_set_lockdep_class(irq, &gpiochip_irq_lock_class);
> >> ^^^^
> > 
> > That piece of code sets the lockdep class of the gpiochip's interrupts, not
> > the parent interrupt.
> > 
> > Found out the hard way by adding some debug code ;-)
> [..]
> > 
> > However, I cannot reproduce the problem on sh73a0/kzm9g with
> > s2ram on a current tree (renesas-drivers-2015-05-19-v4.1-rc4 from
> > (https://git.kernel.org/cgit/linux/kernel/git/geert/renesas-drivers.git), using
> > 
> > CONFIG_LOCKDEP_SUPPORT=y
> > CONFIG_LOCKDEP=y
> > CONFIG_DEBUG_LOCKDEP=y
> > CONFIG_PROVE_LOCKING=y
> > 
> > Wake-up from gpio-keys works fine, no scary messages.
> > 
> >> commit e45d1c80c0eee88e82751461e9cac49d9ed287bc
> >> Author: Linus Walleij <linus.walleij@linaro.org>
> >> Date:   Tue Apr 22 14:01:46 2014 +0200
> >>
> >>      gpio: put GPIO IRQs into their own lock clas
> >>
> >> added in Kernel v3.16
> >>
> >> Roger, can you confirm that you've observed this issue with latest kernel, pls?
> > 
> > Yes please. Thanks!

Issue is reproducible on v4.1-rc6

> 
> Unfortunately, I was able to reproduce it, but have no clue how to fix it gracefully.
> lockdep_set_class_and_subclass(..,gpio_chip->base)?
> 
> HW configuration which generates lockdep warning:
> 
> [SOC GPIO bankA.gpioX] <- irq - [pcf875x.gpioY] <- irq - DevZ.enable_irq_wake(pcf_gpioY_irq);
> 
> There stacked GPIO chips, but gpiolib uses only one lockdep class for all GPIOirqchips -
> - gpiochip_irq_lock_class.

If this is a gpiolib core issue are we (dra7-evm) the only stacked GPIO users facing
this problem?

Linus/Alexandre/Geert,

Please advise what can be done for v4.1. The warning is annoying for dra7-evm users.
Should we temporarily revert the patch even though it is correct and add it back when the
gpiolib core issue is fixed?

cheers,
-roger
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