From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933430Ab2DKV02 (ORCPT ); Wed, 11 Apr 2012 17:26:28 -0400 Received: from cantor2.suse.de ([195.135.220.15]:33500 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933381Ab2DKV01 (ORCPT ); Wed, 11 Apr 2012 17:26:27 -0400 Date: Wed, 11 Apr 2012 23:26:22 +0200 From: Michal Hocko To: Andrew Morton Cc: Glauber Costa , linux-kernel@vger.kernel.org, devel@openvz.org, linux-mm@kvack.org, cgroups@vger.kernel.org, Johannes Weiner , kamezawa.hiroyu@jp.fujitsu.com, Greg Thelen , Suleiman Souhlal , Linus Torvalds Subject: Re: [PATCH] remove BUG() in possible but rare condition Message-ID: <20120411212621.GD24831@tiehlicka.suse.cz> References: <1334167824-19142-1-git-send-email-glommer@parallels.com> <20120411132635.bfddc6bd.akpm@linux-foundation.org> <4F85EEED.1090906@parallels.com> <20120411141244.2839d9a8.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120411141244.2839d9a8.akpm@linux-foundation.org> 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 On Wed 11-04-12 14:12:44, Andrew Morton wrote: > On Wed, 11 Apr 2012 17:51:57 -0300 > Glauber Costa wrote: > > > On 04/11/2012 05:26 PM, Andrew Morton wrote: > > >> > > >> > failed: > > >> > - BUG(); > > >> > unlock_page(page); > > >> > page_cache_release(page); > > >> > return NULL; > > > Cute. > > > > > > AFAICT what happened was that in my April 2002 rewrite of this code I > > > put a non-fatal buffer_error() warning in that case to tell us that > > > something bad happened. > > > > > > Years later we removed the temporary buffer_error() and mistakenly > > > replaced that warning with a BUG(). Only it*can* happen. > > > > > > We can remove the BUG() and fix up callers, or we can pass retry=1 into > > > alloc_page_buffers(), so grow_dev_page() "cannot fail". Immortal > > > functions are a silly fiction, so we should remove the BUG() and fix up > > > callers. > > > > > Any particular caller you are concerned with ? > > Didn't someone see a buggy caller in btrfs? No I missed that __getblk (__getblk_slow) returns NULL only if grow_buffers < 0 while it returns 0 for the allocation failure. Sorry for confusion. -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic