linux-kernel - Re: [PATCH] powerpc/mm: bail out early when flushing TLB page

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Date:	Fri, 30 Jan 2015 15:53:01 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Arseny Solokha <asolokha@...kras.ru>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc/mm: bail out early when flushing TLB page

On Fri, 2015-01-30 at 19:08 +0700, Arseny Solokha wrote:
> MMU_NO_CONTEXT is conditionally defined as 0 or (unsigned int)-1.

For nohash it is specifically -1.

>  However, in __flush_tlb_page() a corresponding variable is only tested
> for open coded 0, which can cause NULL pointer dereference if `mm'
> argument was legitimately passed as such.
> 
> Bail out early in case the first argument is NULL, thus eliminate confusion
> between different values of MMU_NO_CONTEXT and avoid disabling and then
> re-enabling preemption unnecessarily.

How did you notice this?  Did you see an oops, or was it code
inspection?  I'm wondering what codepath gets here with mm == NULL.

-Scott


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