linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <alpine.DEB.2.11.1411200059410.3909@nanos>
Date:	Thu, 20 Nov 2014 01:00:51 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andy Lutomirski <luto@...capital.net>
cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Jones <davej@...hat.com>, Don Zickus <dzickus@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: frequent lockups in 3.18rc4

On Wed, 19 Nov 2014, Andy Lutomirski wrote:
> On Wed, Nov 19, 2014 at 3:09 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > Sorry, I can't follow your argumentation here.
> >
> > pcpu_alloc()
> >    ....
> > area_found:
> >    ....
> >
> >         /* clear the areas and return address relative to base address */
> >         for_each_possible_cpu(cpu)
> >                 memset((void *)pcpu_chunk_addr(chunk, cpu, 0) + off, 0, size);
> >
> > How would that memset fail to establish the mapping, which is
> > btw. already established via:
> >
> >      pcpu_populate_chunk()
> >
> > already before that memset?
> 
> I think that this will map them into init_mm->pgd and
> current->active_mm->pgd, but it won't necessarily map them into the
> rest of the pgds.

And why would mapping them into the kernel mapping, i.e. init_mm not
be sufficient?

We are talking about kernel memory and not some random user space
mapping.

Thanks,

	tglx
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