linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141121123434.279c5613@gandalf.local.home>
Date:	Fri, 21 Nov 2014 12:34:34 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>, Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <peterz@...radead.org>,
	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 Fri, 21 Nov 2014 09:19:02 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, Nov 21, 2014 at 9:08 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> >
> > Actually, in_nmi() is now safe for vmalloc faults. In fact, it handles the
> > clobbering of the cr2 register just fine.
> 
> That's not what I object to and find incorrect wrt NMI.

I was commenting about the WARN_ON() itself.

> 
> Compare the simple and correct 32-bit code to the complex and
> incorrect 64-bit code.
> 
> In particular, look at how the 32-bit code relies *entirely* on hardware state.
> 
> Then look at where the 64-bit code does not.

I see. You have issues with the use of current->active_mm instead of
just doing a read_cr3() (and I'm sure other things).

Doing a series of git blame, 64 bit has been like that since 2005 (start
of git).

Looks to me we have more work to do with the merging of 64 bit and 32
bit. Perhaps 64 bit can become more like 32 bit.

-- Steve
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