linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Fri, 21 Nov 2014 22:11:50 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	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>
Subject: Re: frequent lockups in 3.18rc4

On Fri, 21 Nov 2014, Linus Torvalds wrote:
> On Fri, Nov 21, 2014 at 12:16 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > I don't think that works on 32bit. See the magic in
> > vmalloc_sync_one().
> 
> Heh. I guess we could just add a wrapper around this crap, and make it
> very clear that the paravirt case is a horrible horrible hack.
> 
> Something like
> 
>    #define set_one_pgd_entry(entry,pgdp) (pgdp)->pgd = (entry)
> 
> for the regular case, and then for paravirt we do something very
> explicitly horrid, like
> 
>    #ifdef CONFIG_PARAVIRT
>    #ifdef CONFIG_X86_32
>    // The pmd is the top-level page directory on non-PAE x86, nested
> inside pgd/pud
>    #define set_one_pgd_entry(entry,pgdp) set_pmd((pmd_t *)(pgdp),
> (pmd_t) { entry } )
>    #else
>    #define set_one_pgd_entry(entry, pgdp) do { set_pgd(pgdp, (pgd_t) {
> entry });  arch_flush_lazy_mmu_mode(); } while (0)
>    #endif
> 
> because on x86-64, there seems to be that whole lazy_mode pv_ops
> craziness (which I'm not at all convinced is needed here, but that's
> what the current code does).

I'm fine with that. I just think it's not horrid enough, but that can
be fixed easily :)

Thanks,

	tglx


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