From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757001Ab2C1AWl (ORCPT ); Tue, 27 Mar 2012 20:22:41 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46902 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755841Ab2C1AWk (ORCPT ); Tue, 27 Mar 2012 20:22:40 -0400 Date: Tue, 27 Mar 2012 17:26:22 -0700 From: Andrew Morton To: Dave Jones Cc: viro@zeniv.linux.org.uk, Linux Kernel Subject: Re: suppress page allocation failure warnings from sys_listxattr Message-Id: <20120327172622.827fd6ab.akpm@linux-foundation.org> In-Reply-To: <20120328001550.GA3077@redhat.com> References: <20120313182220.GA11500@redhat.com> <20120327155149.d41a235b.akpm@linux-foundation.org> <20120328001550.GA3077@redhat.com> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Mar 2012 20:15:50 -0400 Dave Jones wrote: > On Tue, Mar 27, 2012 at 03:51:49PM -0700, Andrew Morton wrote: > > On Tue, 13 Mar 2012 14:22:20 -0400 > > Dave Jones wrote: > > > > > This size is user controllable, and so it's trivial for someone to trigger a > > > stream of order:4 page allocation errors. > > > > > > Signed-off-by: Dave Jones > > > > > > --- > > > There's also a similar problem in setxattr, but I'm not sure how we want > > > to pass NOWARN down to memdup_user. Thoughts ? > > > > > > diff --git a/fs/xattr.c b/fs/xattr.c > > > index 82f4337..544df90 100644 > > > --- a/fs/xattr.c > > > +++ b/fs/xattr.c > > > @@ -496,7 +496,7 @@ listxattr(struct dentry *d, char __user *list, size_t size) > > > if (size) { > > > if (size > XATTR_LIST_MAX) > > > size = XATTR_LIST_MAX; > > > - klist = kmalloc(size, GFP_KERNEL); > > > + klist = kmalloc(size, __GFP_NOWARN | GFP_KERNEL); > > > if (!klist) > > > return -ENOMEM; > > > } > > > > hm. The patch is good, but one would hope that it isn't "trivial" to > > trigger a page allocation failure for a kmalloc(65536, GFP_KERNEL) - > > the VM is supposed to be able to handle that. > > > > Is it really *that* easy, or is Something Unusual happening with that > > machine? > > Well, the unusual thing was that I was fuzzing system calls for a few hours. > > My fuzzing tool was able to trigger these very easily after an hour or two > of uptime and memory had fragmented a little, so yeah, quite trivial. > /* * PAGE_ALLOC_COSTLY_ORDER is the order at which allocations are deemed * costly to service. That is between allocation orders which should * coelesce naturally under reasonable reclaim pressure and those which * will not. */ #define PAGE_ALLOC_COSTLY_ORDER 3 Death to magic numbers :(