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

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Message-ID: <54CC579D.1070709@kb.kras.ru>
Date:	Sat, 31 Jan 2015 11:18:37 +0700
From:	Arseny Solokha <asolokha@...kras.ru>
To:	Scott Wood <scottwood@...escale.com>
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.

Just a code inspection. It didn't seemed right at the first glance.

Arsény


>
> -Scott
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