From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id 456976B0037 for ; Wed, 18 Dec 2013 20:04:32 -0500 (EST) Received: by mail-pa0-f47.google.com with SMTP id kq14so419299pab.6 for ; Wed, 18 Dec 2013 17:04:31 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id xa2si1262430pab.200.2013.12.18.17.04.30 for ; Wed, 18 Dec 2013 17:04:30 -0800 (PST) Date: Wed, 18 Dec 2013 17:04:29 -0800 From: Andrew Morton Subject: Re: [PATCH] mm/rmap: fix BUG at rmap_walk Message-Id: <20131218170429.0858bb069d51a469e8c237d8@linux-foundation.org> In-Reply-To: <20131219005805.GA25161@lge.com> References: <1387412195-26498-1-git-send-email-liwanp@linux.vnet.ibm.com> <20131218162858.6ec808c067baf4644532e110@linux-foundation.org> <20131219005805.GA25161@lge.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Joonsoo Kim Cc: Wanpeng Li , Sasha Levin , Hugh Dickins , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, 19 Dec 2013 09:58:05 +0900 Joonsoo Kim wrote: > On Wed, Dec 18, 2013 at 04:28:58PM -0800, Andrew Morton wrote: > > On Thu, 19 Dec 2013 08:16:35 +0800 Wanpeng Li wrote: > > > > > page_get_anon_vma() called in page_referenced_anon() will lock and > > > increase the refcount of anon_vma, page won't be locked for anonymous > > > page. This patch fix it by skip check anonymous page locked. > > > > > > [ 588.698828] kernel BUG at mm/rmap.c:1663! > > > > Why is all this suddenly happening. Did we change something, or did a > > new test get added to trinity? > > It is my fault. > I should remove this VM_BUG_ON() since rmap_walk() can be called > without holding PageLock() in this case. > > I think that adding VM_BUG_ON() to each rmap_walk calllers is better > than this patch, because, now, rmap_walk() is called by many places and > each places has different contexts. I don't think that putting the assertion into the caller makes a lot of sense, particularly if that code just did a lock_page()! If a *callee* needs PageLocked() then that callee should assert that the page is locked. So VM_BUG_ON(!PageLocked(page)); means "this code requires that the page be locked". And if that code requires PageLocked(), there must be reasons for this. Let's also include an explanation of those reasons. -- 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