From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.3 required=3.0 tests=DATE_IN_PAST_06_12, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 797A4C43387 for ; Sat, 22 Dec 2018 16:59:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5085221A48 for ; Sat, 22 Dec 2018 16:59:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388199AbeLVQ76 (ORCPT ); Sat, 22 Dec 2018 11:59:58 -0500 Received: from 178.115.242.59.static.drei.at ([178.115.242.59]:59165 "EHLO mail.osadl.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732597AbeLVQ75 (ORCPT ); Sat, 22 Dec 2018 11:59:57 -0500 Received: by mail.osadl.at (Postfix, from userid 1001) id B9FF05C075C; Sat, 22 Dec 2018 09:04:21 +0100 (CET) Date: Sat, 22 Dec 2018 09:04:21 +0100 From: Nicholas Mc Guire To: David Rientjes Cc: Nicholas Mc Guire , Andrew Morton , Chintan Pandya , Michal Hocko , Andrey Ryabinin , Arun KS , Joe Perches , "Luis R. Rodriguez" , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] mm: vmalloc: do not allow kzalloc to fail Message-ID: <20181222080421.GB26155@osadl.at> References: <1545337437-673-1-git-send-email-hofrat@osadl.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 21, 2018 at 01:58:39PM -0800, David Rientjes wrote: > On Thu, 20 Dec 2018, Nicholas Mc Guire wrote: > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 871e41c..1c118d7 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1258,7 +1258,7 @@ void __init vmalloc_init(void) > > > > /* Import existing vmlist entries. */ > > for (tmp = vmlist; tmp; tmp = tmp->next) { > > - va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT); > > + va = kzalloc(sizeof(*va), GFP_NOWAIT | __GFP_NOFAIL); > > va->flags = VM_VM_AREA; > > va->va_start = (unsigned long)tmp->addr; > > va->va_end = va->va_start + tmp->size; > > Hi Nicholas, > > You're right that this looks wrong because there's no guarantee that va is > actually non-NULL. __GFP_NOFAIL won't help in init, unfortunately, since > we're not giving the page allocator a chance to reclaim so this would > likely just end up looping forever instead of crashing with a NULL pointer > dereference, which would actually be the better result. > tried tracing the __GFP_NOFAIL path and had concluded that it would end in out_of_memory() -> panic("System is deadlocked on memory\n"); which also should point cleanly to the cause - but I´m actually not that sure if that trace was correct in all cases. > You could do > > BUG_ON(!va); > > to make it obvious why we crashed, however. It makes it obvious that the > crash is intentional rather than some error in the kernel code. makes sense - that atleast makes it imediately clear from the code that there is no way out from here. thx! hofrat From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by kanga.kvack.org (Postfix) with ESMTP id 5FDDC8E0001 for ; Sat, 22 Dec 2018 03:04:32 -0500 (EST) Received: by mail-wm1-f72.google.com with SMTP id r11so2663951wmg.1 for ; Sat, 22 Dec 2018 00:04:32 -0800 (PST) Received: from mail.osadl.at (178.115.242.59.static.drei.at. [178.115.242.59]) by mx.google.com with ESMTP id u187si9604652wmf.22.2018.12.22.00.04.30 for ; Sat, 22 Dec 2018 00:04:30 -0800 (PST) Date: Sat, 22 Dec 2018 09:04:21 +0100 From: Nicholas Mc Guire Subject: Re: [PATCH RFC] mm: vmalloc: do not allow kzalloc to fail Message-ID: <20181222080421.GB26155@osadl.at> References: <1545337437-673-1-git-send-email-hofrat@osadl.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Nicholas Mc Guire , Andrew Morton , Chintan Pandya , Michal Hocko , Andrey Ryabinin , Arun KS , Joe Perches , "Luis R. Rodriguez" , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri, Dec 21, 2018 at 01:58:39PM -0800, David Rientjes wrote: > On Thu, 20 Dec 2018, Nicholas Mc Guire wrote: > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 871e41c..1c118d7 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -1258,7 +1258,7 @@ void __init vmalloc_init(void) > > > > /* Import existing vmlist entries. */ > > for (tmp = vmlist; tmp; tmp = tmp->next) { > > - va = kzalloc(sizeof(struct vmap_area), GFP_NOWAIT); > > + va = kzalloc(sizeof(*va), GFP_NOWAIT | __GFP_NOFAIL); > > va->flags = VM_VM_AREA; > > va->va_start = (unsigned long)tmp->addr; > > va->va_end = va->va_start + tmp->size; > > Hi Nicholas, > > You're right that this looks wrong because there's no guarantee that va is > actually non-NULL. __GFP_NOFAIL won't help in init, unfortunately, since > we're not giving the page allocator a chance to reclaim so this would > likely just end up looping forever instead of crashing with a NULL pointer > dereference, which would actually be the better result. > tried tracing the __GFP_NOFAIL path and had concluded that it would end in out_of_memory() -> panic("System is deadlocked on memory\n"); which also should point cleanly to the cause - but I�m actually not that sure if that trace was correct in all cases. > You could do > > BUG_ON(!va); > > to make it obvious why we crashed, however. It makes it obvious that the > crash is intentional rather than some error in the kernel code. makes sense - that atleast makes it imediately clear from the code that there is no way out from here. thx! hofrat