On 01/02/2019 08:45, Julien Thierry wrote: [...] >> +Kernel preemption >> +================= >> +When returning from interrupt context, you should call either of >> +preempt_schedule() or preempt_schedule_irq() if preemption is enabled >> +and need_resched() is true. >> + > > I don't think preempt_schedule() is really an option for a return from > interrupt. First thing preempt_schedule() does is: > > if (likely(!preemptible())) > return; > > And preemptible() is: > > preempt_count() == 0 && !irqs_disabled() > > Generally on return from interrupt context interrupts are disabled, so > we would never be preemptible() and preempt_schedule() would just do > nothing. > > Unless I'm missing something. > No, I think you're right. The main reason I still mentioned it here is to be conservative, although I must admit I've started confusing what we have vs what we used to have since my dive into the history. If I look at some archs that don't use preempt_schedule_irq() (e.g. alpha, unicore32), they seem to be calling schedule() directly - but I don't see any (*current*) user of preempt_schedule() on interrupt return. preempt_schedule() still has this comment attached to it: * this is the entry point to schedule() from in-kernel preemption * off of preempt_enable. Kernel preemptions off return from interrupt * occur there and call schedule directly. So I might just remove the mention to preempt_schedule() in the doc and also change the comment. Thanks, Valentin
