linux-kernel - Re: [PATCH v2 10/10] kernel: might_fault does not imply might

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Message-ID: <20130522101610.GL18810@twins.programming.kicks-ass.net>
Date:	Wed, 22 May 2013 12:16:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	David Howells <dhowells@...hat.com>,
	Hirokazu Takata <takata@...ux-m32r.org>,
	Michal Simek <monstr@...str.eu>,
	Koichi Yasutake <yasutake.koichi@...panasonic.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org, linux-m32r@...linux-m32r.org,
	linux-m32r-ja@...linux-m32r.org, microblaze-uclinux@...e.uq.edu.au,
	linux-am33-list@...hat.com, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, linux-mm@...ck.org,
	kvm@...r.kernel.org, rostedt@...dmis.org
Subject: Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep

On Wed, May 22, 2013 at 12:47:09PM +0300, Michael S. Tsirkin wrote:
> >  
> > +static inline bool __can_fault(void)
> > +{
> > +	/*
> > +	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
> > +	 * holding the mmap_sem, this is safe because kernel memory doesn't
> > +	 * get paged out, therefore we'll never actually fault, and the
> > +	 * below annotations will generate false positives.
> > +	 */
> > +	if (segment_eq(get_fs(), KERNEL_DS))
> > +		return false;
> > +
> > +	if (in_atomic() /* || pagefault_disabled() */)
> 
> One question here: I'm guessing you put this comment here
> for illustrative purposes, implying code that will
> be enabled in -rt?
> We don't want it upstream I think, right?

Right, and as a reminder that when we do this we need to add a patch to
-rt. But yeah, we should have a look and see if its worth pulling those
patches from -rt into mainline in some way shape or form. They're big
but trivial IIRC.

I'm fine with you leaving that comment out though.. 
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