On 2021-03-17 15:38:52 [+0100], Thomas Gleixner wrote: > With interrupt force threading all device interrupt handlers are invoked > from kernel threads. Contrary to hard interrupt context the invocation only > disables bottom halfs, but not interrupts. This was an oversight back then > because any code like this will have an issue: > > thread(irq_A) > irq_handler(A) > spin_lock(&foo->lock); > > interrupt(irq_B) > irq_handler(B) > spin_lock(&foo->lock);
It will not because both threads will wake_up(thread). It is an issue if - if &foo->lock is shared between a hrtimer and threaded-IRQ - if &foo->lock is shared between a non-threaded and thread-IRQ - if &foo->lock is shared between a printk() in hardirq context and thread-IRQ as I learned today. > This has been triggered with networking (NAPI vs. hrtimers) and console > drivers where printk() happens from an interrupt which interrupted the > force threaded handler. > > Now people noticed and started to change the spin_lock() in the handler to > spin_lock_irqsave() which affects performance or add IRQF_NOTHREAD to the > interrupt request which in turn breaks RT. > > Fix the root cause and not the symptom and disable interrupts before > invoking the force threaded handler which preserves the regular semantics > and the usefulness of the interrupt force threading as a general debugging > tool. > > For not RT this is not changing much, except that during the execution of > the threaded handler interrupts are delayed until the handler > returns. Vs. scheduling and softirq processing there is no difference. > > For RT kernels there is no issue. Acked-by: Sebastian Andrzej Siewior <[email protected]> > Fixes: 8d32a307e4fa ("genirq: Provide forced interrupt threading") > Reported-by: Johan Hovold <[email protected]> > Signed-off-by: Thomas Gleixner <[email protected]> > Cc: Eric Dumazet <[email protected]> > Cc: Sebastian Andrzej Siewior <[email protected]> > Cc: netdev <[email protected]> > Cc: "David S. Miller" <[email protected]> > Cc: Krzysztof Kozlowski <[email protected]> > Cc: Greg Kroah-Hartman <[email protected]> > Cc: Andy Shevchenko <[email protected]> > CC: Peter Zijlstra <[email protected]> > Cc: [email protected] > Cc: netdev <[email protected]> > --- > kernel/irq/manage.c | 4 ++++ > 1 file changed, 4 insertions(+) > > --- a/kernel/irq/manage.c > +++ b/kernel/irq/manage.c > @@ -1142,11 +1142,15 @@ irq_forced_thread_fn(struct irq_desc *de > irqreturn_t ret; > > local_bh_disable(); > + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) > + local_irq_disable(); > ret = action->thread_fn(action->irq, action->dev_id); > if (ret == IRQ_HANDLED) > atomic_inc(&desc->threads_handled); > > irq_finalize_oneshot(desc, action); > + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) > + local_irq_enable(); > local_bh_enable(); > return ret; > } Sebastian
