linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+55aFyt6q7Ed-SS9GeN8jeUZu6yNM14EGyH_8rn8AF2Vv37hg@mail.gmail.com>
Date:	Fri, 21 Nov 2014 12:41:44 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
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, 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).

                Linus
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