Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030336AbaGEAbA (ORCPT ); Fri, 4 Jul 2014 20:31:00 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:36315 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753651AbaGEAa6 (ORCPT ); Fri, 4 Jul 2014 20:30:58 -0400 Date: Sat, 5 Jul 2014 02:30:53 +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] MIPS: Fix incorrect NULL check in local_flush_tlb_page() Message-ID: <20140705003053.GB3404@lianli> References: <1404493623-22705-1-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 Jonas, On Fri, Jul 04, 2014 at 11:52:51PM +0200, Jonas Gorski wrote: > On Fri, Jul 4, 2014 at 7:07 PM, Emil Goode wrote: > > We check that the struct vm_area_struct pointer vma is NULL and > > then dereference it. The intent must have been to check that > > vma is not NULL before we dereference it in the next condition. > > Actually if it is NULL, then it will short-cut and won't dereference > it (because !vma is true it can never become false again), so the > condition would be fine previously. > > But, looking at the code a few lines into branch: > > if (!vma || cpu_context(cpu, vma->vm_mm) != 0) { > unsigned long flags; > int oldpid, newpid, idx; > > #ifdef DEBUG_TLB > printk("[tlbpage<%lu,0x%08lx>]", cpu_context(cpu, > vma->vm_mm), page); > #endif > newpid = cpu_context(cpu, vma->vm_mm) & ASID_MASK; > > it will be then dereferenced here, so the change is actually sensible, > even if the description isn't quite spot-on where it breaks. Sorry, this is what I meant but failed to explain clearly. Perhaps the following is a bit better? 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. 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/