On Thu, Aug 06, 2020 at 08:50:45PM +0200, Thomas Gleixner wrote: > Linus Walleij <linus.walleij@xxxxxxxxxx> writes: > > On Thu, Aug 6, 2020 at 12:20 PM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > > >> So the solution for this driver is either to make the dispatch handler > >> threaded or use the hard interrupt variant of dispatching the > >> demultiplexed GPIO interrupts. > > > > The struct gpio_irq_chip .threaded bool that the patch > > sets just instructs the gpio core to issue > > irq_set_nested_thread(irq, 1) on the child IRQ. > > > > This is a driver of type "struct siox_driver" handling the > > IRQ through the special .get_data callback supplied in the > > driver struct and it calls handle_nested_irq(irq) so with > > this fix it percolated up to the parent as intended. > > > > So far so good. So I think the patch should be applied. > > > > But what is behind this .get_data() callback for siox drivers? > > > > The siox driver framework in drivers/siox dispatches calls > > to .get_data() from a polling thread which is just some ordinary > > kthread. It looks like this because the SIOX (I think) needs > > to do polled I/O. (drivers/siox/siox-core.c) > > > > So this is a thread but it is not an irq thread from the irq core, > > however it is treated like such by the driver, and in a way what > > happens is events, just polled by a thread. > > As Uwe just explained. > > > So when we call handle_nested_irq() ... we are not really > > calling that from an irq handler. > > > > I don't know if the IRQ core even sees a difference between which > > thread it gets interfaced with. I suppose it does? :/ > > handle_nested_irq() does not care. It cares about thread context, > external reentrancy protection for the same nested interrupt and that > the nested interrupt has a thread handler. > > The latter is what goes belly up because w/o that threaded bit set the > GPIO core fails to set nested thread. So if a consumer requests an > interrupt with request_any_context_irq() then that fails to select > thread mode which means the threaded handler is not set causing > handle_nested_irq() to fail. For a caller of request_threaded_irq() that passes a relevant hardirq handler the hardirq handler is never called but request_threaded_irq() doesn't fail. The handler is just replaced by irq_nested_primary_handler in __setup_irq(). Is that a bug? (I didn't test, just read the code, so I might have missed something.) > The polling kthread is a slight but clever abomination, but it just > works because it provides thread context and cannot run concurrently. I think this is the first time you called any of my code "clever" :-) > So Ahmad's patch is correct, just the changelog needs polishing. Trying to be constructive, here is my suggested changelog: gpio: siox: explicitly only support threaded irqs The gpio-siox driver uses handle_nested_irq() to implement its interrupt support. This is only capable to handle threaded irq actions. For a hardirq action it triggers a NULL pointer oops. (It calls action->thread_fn which is NULL then.) So prevent registration of a hardirq action by setting gpio_irq_chip::threaded to true. Does this address all your concerns? Is this bad enough to justify sending this patch to stable? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |
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