Re: frequent lockups in 3.18rc4

From: Dave Jones
Date: Thu Dec 11 2014 - 22:04:29 EST

On Thu, Dec 11, 2014 at 01:49:17PM -0800, Linus Torvalds wrote:

> Anyway, you might as well stop bisecting. Regardless of where it lands
> in the remaining pile, it's not going to give us any useful
> information, methinks.
> I'm stumped.

yeah, likewise. I don't recall any bug that's given me this much headache.
I don't think it's helped that the symptoms are vague enough that a
number of people have thought they've seen the same thing, which have
turned out to be unrelated incidents. At least some of those have
gotten closure though it seems.

> Maybe it's worth it to concentrate on just testing current kernels,
> and instead try to limit the triggering some other way. In particular,
> you had a trinity run that was *only* testing lsetxattr(). Is that
> really *all* that was going on? Obviously trinity will be using
> timers, fork, and other things? Can you recreate that lsetxattr thing,
> and just try to get as many problem reports as possible from one
> particular kernel (say, 3.18, since that should be a reasonable modern
> base with hopefully not a lot of other random issues)?

I'll let it run overnight, but so far after 4hrs, on .18 it's not done

> Together with perhaps config checks. You've done some those already.
> Did it reproduce without preemption, for example?

Next kernel build I try, I'll turn that off. I don't remember if
we've already tried that. I *think* we just tried the non-preempt rcu
stuff, but not "no preemption at all". I wish I'd kept better notes
about everything tried so far too, but I hadn't anticipated this
dragging out so long. Live and learn..


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