From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Sun, 06 Jul 2014 00:50:56 +0200 (CEST) Received: from mail-la0-f49.google.com ([209.85.215.49]:57320 "EHLO mail-la0-f49.google.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6860024AbaGEWuwgJoL6 (ORCPT ); Sun, 6 Jul 2014 00:50:52 +0200 Received: by mail-la0-f49.google.com with SMTP id gf5so1880327lab.8 for ; Sat, 05 Jul 2014 15:50:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=AK3s3ZUhohxLIJqDZwluRsTTfE2eFIoSk7Ci4zBKW64=; b=jauhscZnYDMh83jBRCgDeQHJRLvneqdvaX0XmzciGBLM8Z/wXjj3eIdgRch9hMoM6C lDB7Xklt3mcy9diJ8j1yyAPnCC0E3emKkhvtG32yhqmz0qs9UJW4l5ntsmk0mlJGYSN5 EgMuGfvn/CSzPR6YyLM6WPvY0PKD9ISx55g3QBaw7nJgBGKaww7VrK8xVlOBG/A1v9kI uVZZz5Afcqg46sv5Bo/2vi2ltcp0fpaHVAODL5aPd80Kl1e4IdUTWwPsEtsiynXtJVfA 4WEsXu8/pStKAFu94oc31z37S4ibDCj0rLt/011AA01Xws4tkHpq4yBP8RxGyi/A8VpE f8aQ== X-Received: by 10.152.5.230 with SMTP id v6mr15056663lav.33.1404600646936; Sat, 05 Jul 2014 15:50:46 -0700 (PDT) Received: from lianli (c193-14-6-78.cust.tele2.se. [193.14.6.78]) by mx.google.com with ESMTPSA id jv2sm15511403lbc.45.2014.07.05.15.50.45 for (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Sat, 05 Jul 2014 15:50:46 -0700 (PDT) Date: Sun, 6 Jul 2014 00:50:34 +0200 From: Emil Goode To: Jonas Gorski Cc: Ralf Baechle , Paul Gortmaker , John Crispin , MIPS Mailing List , "linux-kernel@vger.kernel.org" , kernel-janitors@vger.kernel.org Subject: Re: [PATCH v2] MIPS: Fix incorrect NULL check in local_flush_tlb_page() Message-ID: <20140705225034.GA12090@lianli> References: <1404584812-12377-1-git-send-email-emilgoode@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 41053 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: emilgoode@gmail.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips Hello, On Sat, Jul 05, 2014 at 09:10:44PM +0200, Jonas Gorski wrote: > On Sat, Jul 5, 2014 at 8:26 PM, Emil Goode wrote: > > We check that the struct vm_area_struct pointer vma is NULL and then > > dereference it a few lines below. The intent must have been to make sure > > that vma is not NULL and then to check the value from cpu_context() for > > the condition to be true. > > > > Signed-off-by: Emil Goode > > --- > > > > v2: Updated the commit message with a better explanation. > > > > arch/mips/mm/tlb-r3k.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/mips/mm/tlb-r3k.c b/arch/mips/mm/tlb-r3k.c > > index d657493..6546758 100644 > > --- a/arch/mips/mm/tlb-r3k.c > > +++ b/arch/mips/mm/tlb-r3k.c > > @@ -158,7 +158,7 @@ void local_flush_tlb_page(struct vm_area_struct *vma, unsigned long page) > > { > > int cpu = smp_processor_id(); > > > > - if (!vma || cpu_context(cpu, vma->vm_mm) != 0) { > > + if (vma && cpu_context(cpu, vma->vm_mm) != 0) { > > Sorry for replying "too late", but grepping through the kernel code I > fail to find any caller that does not dereference vma before calling > (local)flush_tlb_page(). Also both tlb-4k and tlb-8k assume vma cannot > be NULL, so I would say it is safe to assume vma is never NULL, and > the NULL check can be removed completely. > > Also it looks like this "bug" was there since at least 2.6.12, and > never seem to have bitten anyone. Yes, the bug pre-dates GIT history and I agree that it is most unlikely that it ever caused a problem. I will send a new patch that removes the NULL check of vma. Best regards, Emil Goode