linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141118023930.GA2871@redhat.com>
Date:	Mon, 17 Nov 2014 21:39:30 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Mon, Nov 17, 2014 at 06:21:08PM -0800, Linus Torvalds wrote:
 > On Mon, Nov 17, 2014 at 6:09 PM, Dave Jones <davej@...hat.com> wrote:
 > >
 > > After wasting countless hours rolling back to Fedora 20 and gcc 4.8.1,
 > > I saw the exact same trace on 3.17, so now I don't know what to think.
 > 
 > Uhhuh.
 > 
 > Has anything else changed? New trinity tests? If it has happened in as
 > little as ten minutes, and you don't recall having seen this until
 > about a week ago, it does sound like something changed.

Looking at the trinity commits over the last month or so, there's a few
new things, but nothing that sounds like it would trip up a bug like
this. "generate random ascii strings" and "mess with fcntl's after
opening fd's on startup" being the stand-outs. Everything else is pretty
much cleanups and code-motion. There was a lot of work on the code
that tracks mmaps about a month ago, but that shouldn't have had any
visible runtime differences.

<runs git diff>

hm, something I changed not that long ago, which I didn't commit yet,
was that it now runs more child processes than it used to (was 64, now 256)
I've been running like that for a while though. I want to say that was
before .17, but I'm not 100% sure.

So it could be that I'm just generating a lot more load now.
I could drop that back down and see if it 'goes away' or at least
happens less, but it strikes me that there's something here that needs
fixing regardless.

	Dave

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