linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <20141121223309.GC19283@laptop.dumpdata.com>
Date:	Fri, 21 Nov 2014 17:33:09 -0500
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	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>,
	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>,
	xen-devel@...ts.xenproject.org
Subject: Re: frequent lockups in 3.18rc4

On Fri, Nov 21, 2014 at 08:51:43PM +0100, Thomas Gleixner wrote:
> On Fri, 21 Nov 2014, Linus Torvalds wrote:
> > Here's the simplified end result. Again, this is TOTALLY UNTESTED. I
> > compiled it and verified that the code generation looks like what I'd
> > have expected, but that's literally it.
> > 
> >   static noinline int vmalloc_fault(unsigned long address)
> >   {
> >         pgd_t *pgd_dst;
> >         pgdval_t pgd_entry;
> >         unsigned index = pgd_index(address);
> > 
> >         if (index < KERNEL_PGD_BOUNDARY)
> >                 return -1;
> > 
> >         pgd_entry = init_mm.pgd[index].pgd;
> >         if (!pgd_entry)
> >                 return -1;
> > 
> >         pgd_dst = __va(PAGE_MASK & read_cr3());
> >         pgd_dst += index;
> > 
> >         if (pgd_dst->pgd)
> >                 return -1;
> > 
> >         ACCESS_ONCE(pgd_dst->pgd) = pgd_entry;
> 
> This will break paravirt. set_pgd/set_pmd are paravirt functions.
> 
> But I'm fine with breaking it, then you just need to change
> CONFIG_PARAVIRT to 'def_bool n'

That is not very nice.
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