On Fri 25 Sep 2020 at 15:44, Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> wrote: > On 2020-09-25 11:11:42 [+0200], Jerome Brunet wrote: >> I'm not sure about this. >> As you have explained on IRC, I understand that IRQF_ONESHOT is causing >> trouble with RT as the hard IRQ part of the thread will not be migrated >> to a thread. That was certainly not the intent when putting this flag. > > That is my understanding as well. > >> This seems pretty unsafe to me. Maybe we could improve the driver so it >> copes with this case gracefully. ATM, I don't think it would. > > Running the primary handler in hardirq context is bad, because it > invokes meson_mmc_request_done() at the very end. And here: > - mmc_complete_cmd() -> complete_all() > There is a lockdep_assert_RT_in_threaded_ctx() which should trigger. > > - led_trigger_event() -> led_trigger_event() > This should trigger a might_sleep() warning somewhere. > > So removing IRQF_ONESHOT is okay but it should additionally disable the > IRQ source in meson_mmc_irq() and re-enable back in > meson_mmc_irq_thread(). Otherwise the IRQ remains asserted and may fire > multiple times before the thread has a chance to run. Looks like we need to do manually what IRQF_ONESHOT was doing for us :( This brings a few questions: * The consideration you described is not mentioned near the description of IRQF_ONESHOT. Maybe it should so other drivers with same intent don't end up in the same pitfall ? * Why doesn't RT move the IRQ with this flag ? Seems completly unrelated to RT (maybe it is the same documentation problem) * Can't we have flag doing the irq disable in the same way while still allowing to RT to do its magic ? seems better than open coding it in the driver ? > > Sebastian
