[email protected] wrote:
> It comes up with a screaming ksoftirqd - usually /1 but one boot had /0.
> Just sitting there, 100% CPU according to 'top'. Tried 'echo t > /proc/sysrq-trigger' to get
> a trace, but it was always running on the other CPU - even after I reniced
> it down to 19 and launched 2 'for(;;)' C programs to suck the cycles. It would
> be failing to get any CPU - until I did the 'echo t' and then it would be
> "running" again. Anybody got any good debugging ideas here?
>
Huh. I've just been trying to find a problem with events/1 spinning
after boot in current -git. I was worried I'd introduced it, but looks
like there might be a wider problem.
I tracked it down to kernel/workqueue.c:run_workqueue(), where the while
(!list_empty(&cwq->worklist)) loop spins forever. It turns out that the
list_empty test was failing, but cwq->worklist was pointing to itself
(iow, worklist.next points to a self-pointing list node).
I haven't found how it was getting into that state, but the use of
list_del_init(cwq->worklist.next) looks suspect to me.
Curiously, it seems to escape this loop after about 4-5mins, and then
seems well-behaved from then on. And it doesn't always happen.
And, of course, no changes in kernel/workqueue.c since Feb, so whatever
changed was somewhere else, and I guess it could have affected kevent in
the same way.
It always seems to happen on the last CPU; when I run the kernel as Xen
guest with 4 vcpus, it happens on events/3.
J
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