linux-kernel - Re: [PATCH] irq: Request and release resources for chained IRQs

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Date:   Fri, 7 Dec 2018 12:51:39 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Walleij <linus.walleij@...aro.org>
cc:     Marc Zyngier <marc.zyngier@....com>,
        Jason Cooper <jason@...edaemon.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Hans Verkuil <hverkuil@...all.nl>
Subject: Re: [PATCH] irq: Request and release resources for chained IRQs

On Fri, 7 Dec 2018, Linus Walleij wrote:

Sorry for answering late.

> On Thu, Nov 29, 2018 at 2:31 PM Linus Walleij <linus.walleij@...aro.org> wrote:
> >
> > This irqchip is in drivers/pinctrl/qcom/pinctrl-msm.c and known
> > as TLMM.

TLMM == Totally Lost Manufacturer Mess?

> > However, the irqchip core helpers in GPIO assumes that
> > the .irq_request_resources() callback is always called before
> > .irq_enable(), and the latter is where module refcount and
> > also gpiochip_lock_as_irq() is normally called.
> >
> > When .irq_enable() is called without .irq_request_resources()
> > having been called first, it seems like we are enabling
> > an IRQ on a GPIO line that has not first been locked to be
> > used as IRQ and we get the above warning. This happens since
> > as of
> > commit 461c1a7d4733d ("gpiolib: override irq_enable/disable")
> > this is strictly assumed for all GPIO-based IRQs.
> >
> > As it seems reasonable to assume that .irq_request_resources()
> > is always strictly called before .irq_enable(), we add the
> > irq_[request|release]_resources() functions to the internal
> > API and call them also when adding a chained irqchip to
> > an IRQ.
> >
> > I am a bit uncertain about the call site for
> > irq_released_resources() inside chip.c, but it appears this
> > path is for uninstalling a chained handler.

You cannot invoke those callbacks from __irq_do_set_handler() as that is
holding the irq descriptor lock with interrupts disabled.

The calling convention for irq_released_resources() is that it's called
with the bus lock held (if the chip provides the bus lock callbacks), but
definitely not with desc->lock held.

Needs more thought. Btw, the uninstall path does not invoke irq_deactive()
either.... I so hate that chained handler mess....

Thanks,

	tglx