linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Fri, 21 Nov 2014 14:23:01 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andy Lutomirski <luto@...capital.net>, Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	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 11:06:41 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:
 
>   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;

Should we at least check to see if it is present?

	if (!(pgd_entry & 1))
		return -1;

?

-- Steve

> 
>         pgd_dst = __va(PAGE_MASK & read_cr3());
>         pgd_dst += index;
> 
>         if (pgd_dst->pgd)
>                 return -1;
> 
>         ACCESS_ONCE(pgd_dst->pgd) = pgd_entry;
>         return 0;
>   }
>   NOKPROBE_SYMBOL(vmalloc_fault);
> 
> Hmm? Does anybody see anything fundamentally wrong with this?
> 
>                      Linus

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