From: Thomas Gleixner
Date: Fri Aug 28 2015 - 15:43:08 EST

On Tue, 25 Aug 2015, Felipe Balbi wrote:
> Hi Ingo,

Thanks for not cc'ing the irq maintainer ....

> I'm facing an issue with CONFIG_DEBUG_SHIRQ and pm_runtime when using
> devm_request_*irq().
> If we using devm_request_*irq(), that irq will be freed after device
> drivers' ->remove() gets called. If on ->remove(), we're calling
> pm_runtime_put_sync(); pm_runtime_disable(), device's clocks might get
> gated and, because we do an extra call to the device's IRQ handler when
> CONFIG_DEBUG_SHIRQ=y, we might trigger an abort exception if, inside the
> IRQ handler, we try to read a register which is clocked by the device's
> clock.
> This is, of course, really old code which has been in tree for many,
> many years. I guess nobody has been running their tests in the setup
> mentioned above (CONFIG_DEBUG_SHIRQ=y, pm_runtime_put_sync() on
> ->remove(), a register read on IRQ handler, and a shared IRQ handler),
> so that's why we never caught this before.
> Disabling CONFIG_DEBUG_SHIRQ, of course, makes the problem go away, but
> if driver *must* be ready to receive, and handle, an IRQ even during
> module removal, I wonder what the IRQ handler should do. We can't, in
> most cases, call pm_runtime_put_sync() from IRQ handler.

Well, a shared interrupt handler must handle this situation, no matter
what. Assume the following:

irqreturn_t dev_irq(int irq, void *data)
struct devdata *dd = data;
u32 state;

state = readl(dd->base);

void module_exit(void)
/* Write to the device interrupt register */
* After this point the device does not longer
* raise an interrupt

If the other device which shares the interrupt line raises an
interrupt after the unmap and before free_irq() removed the device
handler from the irq, the machine is toast, because the dev_irq
handler is still called.

If the handler is shut down after critical parts of the driver/device
are shut down, then you can

- either can change the setup/teardown ordering


- or have a proper flag in the private data which tells the interrupt
handler to sod off.

irqreturn_t dev_irq(int irq, void *data)
struct devdata *dd = data;

if (dd->shutdown)
return IRQ_NONE;

void module_exit(void)
dd->shutdown = 1;

/* On an SMP machine you also need: */

So for the problem at hand, the devm magic needs to make sure that the
crucial parts are still alive when the devm allocated irq is released.

I have no idea how that runtime PM stuff is integrated into devm (I
fear not at all), so it's hard to give you a proper advise on that.


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