Messages in this thread | | | Date | Fri, 28 Aug 2015 21:42:26 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: CONFIG_DEBUG_SHIRQ and PM |
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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 */ disable_device_irq(dd->base); /* * After this point the device does not longer * raise an interrupt */ iounmap(dd->base); free_irq();
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
disable_device_irq(dd->base); free_irq(); iounmap(dd->base);
- 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) { disable_device_irq(dd->base); dd->shutdown = 1;
/* On an SMP machine you also need: */ synchronize_irq(dd->irq);
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.
Thanks,
tglx
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