* David Howells (dhowells@xxxxxxxxxx) wrote: > Nicolas Pitre <nico@xxxxxxx> wrote: > > > > I mean, the darned thing is called from sched_clock(), which can be > > > concurrently called on separate CPUs and which can be called from > > > interrupt context (with an arbitrary nesting level!) while it was running > > > in process context. > > > > Yes! And this is so on *purpose*. Please take some time to read the > > comment that goes along with it, and if you're still not convinced then > > look for those explanation emails I've already posted. > > I agree with Nicolas on this. It's abominably clever, but I think he's right. > > The one place I remain unconvinced is over the issue of preemption of a process > that is in the middle of cnt32_to_63(), where if the preempted process is > asleep for long enough, I think it can wind time backwards when it resumes, but > that's not a problem for the one place I want to use it (sched_clock()) because > that is (almost) always called with preemption disabled in one way or another. > > The one place it isn't is a debugging case that I'm not too worried about. > I am also concerned about the non-preemption off case. Then I think the function should document that it must be called with preempt disabled. Mathieu > > > /* > > > * Caller must provide locking to protect *caller_state > > > */ > > > > NO! This is meant to be LOCK FREE! > > Absolutely. > > David -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
