linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Thu, 11 Dec 2014 22:03:43 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

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
anything.

 > 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..

	Dave

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