linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CALCETrVLrXOZNY6Xha+TukJMTb2ni70FN==rL8KHM6FrMwWzVQ@mail.gmail.com>
Date:	Tue, 16 Dec 2014 16:41:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>, Dave Jones <davej@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Tue, Dec 16, 2014 at 4:00 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Tue, Dec 16, 2014 at 3:02 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> OK, should we just stick it in the x86 tree and see if anything
>> explodes? ;-)
>
> Gaah, I got confused about the patches.
>
> And something did explode, it showed some Xen nasties. Xen has that
> odd "we don't share PMD entries between MM's" thing going on, which
> means that the vmalloc fault thing does actually have to occasionally
> walk two levels rather than just copy the top level. I'm still not
> sure why Xen doesn't share PMD's, since threads that shame the MM
> clearly can share PMD's within Xen, but I gave up on it.

Sounds like it's time to ask Konrad, the source of all Xen understanding :)

Linus, do you have a pointer to whatever version of the patch you tried?

--Andy

>
> That said, making x86-64 use "read_cr3()" instead of
> "current->active_mm" would at least make things a bit safer wrt NMI's
> during the task switch, of course.  So *some* 32/64-bit consolidation
> should be done, but my patch went a bit too far for Xen.
>
>                       Linus



-- 
Andy Lutomirski
AMA Capital Management, LLC
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