From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751232Ab2C1Ej4 (ORCPT ); Wed, 28 Mar 2012 00:39:56 -0400 Received: from ipmail06.adl6.internode.on.net ([150.101.137.145]:6389 "EHLO ipmail06.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750804Ab2C1Ejz (ORCPT ); Wed, 28 Mar 2012 00:39:55 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: Av0EAJOVck95LEyG/2dsb2JhbAA/BrhngQiCCQEBBToNDzMIAxguFCUDIQESG4durAmOHBOKW4UuYwSVYIlQhl6Cew Date: Wed, 28 Mar 2012 15:39:51 +1100 From: Dave Chinner To: Dave Jones , Andrew Morton , viro@zeniv.linux.org.uk, Linux Kernel Subject: Re: suppress page allocation failure warnings from sys_listxattr Message-ID: <20120328043951.GA32741@dastard> References: <20120313182220.GA11500@redhat.com> <20120327155149.d41a235b.akpm@linux-foundation.org> <20120328001550.GA3077@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120328001550.GA3077@redhat.com> 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 Tue, Mar 27, 2012 at 08:15:50PM -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. We've recently been seeing reports of xfsdump trigging a similar allocation failures in the XFS attr code when we are doing hundreds of thousands of attribute lookups to back them up. ad650f5 xfs: fallback to vmalloc for large buffers in xfs_attrmulti_attr_get I think that falling back to vmalloc here is much better solution than failing to retreive the attribute - it will work no matter how fragmented memory gets. That means we don't get incomplete backups occurring after days or months of uptime and successful backups... Cheers, Dave. -- Dave Chinner david@fromorbit.com