Re: [PATCH v5 04/10] PCI: rockchip: fix system hang up if activating CONFIG_DEBUG_SHIRQ

[Brian Norris <briannorris@chromium.org>]

On Thu, Aug 24, 2017 at 02:10:52PM -0700, Dmitry Torokhov wrote:
> On Thu, Aug 24, 2017 at 1:21 PM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> > [+cc Tejun, Dmitry, Michael, Stephen, linux-clk for devm/clk questions]
> >
> > On Wed, Aug 23, 2017 at 03:02:38PM +0800, Shawn Lin wrote:
> >> With CONFIG_DEBUG_SHIRQ enabled, the irq tear down routine
> >> would still access the irq handler registed as a shard irq.
> >> Per the comment within the function of __free_irq, it says
> >> "It's a shared IRQ -- the driver ought to be prepared for
> >> an IRQ event to happen even now it's being freed". However
> >> when failing to probe the driver, it may disable the clock
> >> for accessing the register and the following check for shared
> >> irq state would call the irq handler which accesses the register
> >> w/o the clk enabled. That will hang the system forever.

Side note: why is this driver even requesting a shared IRQ? This is for
rk3399, and the IRQ is a dedicated GIC interrupt for the PCIe
controller. It shouldn't need to be 'shared'.

The problem still might not be *only* theoretical though, since it's
still possible for this non-shared interrupt to
(a) trigger
(b) concurrently, we remove/tear down (including disable clocks)
(c) we service the IRQ      <-- dead, because clock is disabled
(d) if we ever got here... free_irq()

Brian