Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755686AbaGEWuu (ORCPT ); Sat, 5 Jul 2014 18:50:50 -0400 Received: from mail-la0-f51.google.com ([209.85.215.51]:34066 "EHLO mail-la0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753887AbaGEWus (ORCPT ); Sat, 5 Jul 2014 18:50:48 -0400 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) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/