On Thu, 2023-10-26 at 08:49 +0000, Vincent Whitchurch wrote: > On Thu, 2023-10-26 at 09:38 +0200, Johannes Berg wrote: > > On Thu, 2023-10-26 at 07:23 +0000, Vincent Whitchurch wrote: > > > > @@ -839,9 +863,7 @@ static u64 timer_read(struct clocksource *cs) > > > > */ > > > > if (!irqs_disabled() && !in_interrupt() && > > > > !in_softirq() && > > > > !time_travel_ext_waiting) > > > > - time_travel_update_time(time_travel_time + > > > > - TIMER_MULTIPLIER, > > > > - false); > > > > + time_travel_update_time_rel(TIMER_MULTIPLIER); > > > > return time_travel_time / TIMER_MULTIPLIER; > > > > } > > > > > > The reason I hesitated with putting the whole of > > > time_travel_update_time() under local_irq_save() in my attempt was > > > because I didn't quite understand the reason for the !irqs_disabled() > > > condition here and the comment just above it about recursion and things > > > getting messed up. If it's OK to disable interrupts as this patch does, > > > is the !irqs_disabled() condition valid? > > > > Hmm. I was going to say that's different, because it wants to only > > prevent us from doing this while we're *already* in IRQ context, and the > > bug you found is calling timer_read() not in IRQ context, but getting an > > event queued by the signal. > > > > But ... now that I think about it, I have a feeling that this was a > > workaround for the exact same problem, and I just didn't understand it > > at the time? I mean, recursing into our own processing is now impossible > > here after this patch - either we're running normally, or the interrupt > > cannot hit timer_read() in the middle, same as it cannot hit > > time_travel_handle_real_alarm() in the middle now. > > > > Removing that still seems to work with your test, but it's also not a > > good test for this, since there are no devices etc. that could have > > interrupts, not sure how to test it right now? > > > > Maybe I'll add a comment there saying this might no longer be needed? > > I tried removing the !irqs_disabled() check and that blew up pretty > quickly (below) when running the full roadtest suite. It works fine > with your unmodified patch so no need to change the comment. >
Hah, OK. So maybe when/if I remember what happens there or can figure it out again, I can update the comment :) johannes _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um
