From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 31 Jan 2008 23:55:44 -0800 From: Andrew Morton Subject: Re: [patch] NULL pointer check for vma->vm_mm Message-Id: <20080131235544.346b938a.akpm@linux-foundation.org> In-Reply-To: <3fd7d7a70801312339p2a142096p83ed286c81379728@mail.gmail.com> References: <3fd7d7a70801312339p2a142096p83ed286c81379728@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Kenichi Okuyama Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Fri, 1 Feb 2008 16:39:07 +0900 "Kenichi Okuyama" wrote: > Dear all, > > I was looking at the ./mm/rmap.c .. I found that, in function > "page_referenced_one()", > struct mm_struct *mm = vma->vm_mm; > was being refererred without NULL check. > > Though I do agree that this works for most of the cases, I thought it > is better to add > BUG_ON() for case of mm being NULL. > > attached is the patch for this If we dereference NULL then the kernel will display basically the same information as would a BUG, and it takes the same action. So adding a BUG_ON here really doesn't gain us anything. Also, I think vma->vm_mm == 0 is not a valid state, so this just shouldn't happen - the code is OK to assume that a particular invariant is being honoured. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org