Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752258AbZGBANQ (ORCPT ); Wed, 1 Jul 2009 20:13:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751754AbZGBANB (ORCPT ); Wed, 1 Jul 2009 20:13:01 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:51204 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750969AbZGBANA (ORCPT ); Wed, 1 Jul 2009 20:13:00 -0400 Date: Wed, 1 Jul 2009 17:12:49 -0700 From: Andrew Morton To: ebiederm@xmission.com (Eric W. Biederman) Cc: Amerigo Wang , tao.ma@oracle.com, linux-kernel@vger.kernel.org, adobriyan@gmail.com, mtk.manpages@gmail.com, Yasunori Goto , KAMEZAWA Hiroyuki Subject: Re: [RESEND Patch] kcore: remove its pointless size Message-Id: <20090701171249.004968e8.akpm@linux-foundation.org> In-Reply-To: References: <20090613040958.GA2959@cr0> <2375c9f90906160829g3d605836yb4c5b9beeac50c5f@mail.gmail.com> <20090618030051.GA6133@cr0.nay.redhat.com> <20090618044055.GB6133@cr0.nay.redhat.com> <20090622085405.GA6499@cr0.nay.redhat.com> <20090630100850.GD5873@cr0.nay.redhat.com> <20090701144742.6ce3535b.akpm@linux-foundation.org> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; 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 Content-Length: 2753 Lines: 74 On Wed, 01 Jul 2009 16:25:05 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote: > Andrew Morton writes: > > >> index 59b43a0..eca5201 100644 > >> --- a/fs/proc/kcore.c > >> +++ b/fs/proc/kcore.c > >> @@ -405,9 +405,6 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > >> static int __init proc_kcore_init(void) > >> { > >> proc_root_kcore = proc_create("kcore", S_IRUSR, NULL, &proc_kcore_operations); > >> - if (proc_root_kcore) > >> - proc_root_kcore->size = > >> - (size_t)high_memory - PAGE_OFFSET + PAGE_SIZE; > >> return 0; > >> } > >> module_init(proc_kcore_init); > > > > AFAICT this means that proc_root_kcore->size will remain uninitialised > > until a process opens and reads from /proc/kcore. So on initial boot > > the `ls' output will presumably show a size of zero, and this will > > change once /proc/kcore has been read? > > Which is better than showing a random number of dubious relationship > to the size we normally show. That code is just a maintenance problem. Well it's not just that st_size is wrong before the first read. It's also wrong after memory hot-add, up until the next read. > > If so, should we run get_kcore_size() in proc_kcore_init(), perhaps? > > > > In fact, do we need to run get_kcore_size() more than once per boot? > > > > AFAICT we only run kclist_add() during bootup, so if proc_kcore_init() > > is called at the appropriate time, we can permanently cache its result? > > > > In which case get_kcore_size() and kclist_add() can be marked __init. > > > > Maybe that's all wrong - I didn't look terribly closely. > > Memory hot add I expect is the excuse. There is more that could be > done. But this patch is an obvious bit of chipping away nonsense > code. We have the infrastructure to get this right, I think: - run proc_root_kcore->size = get_kcore_size(...) within proc_kcore_init() - register a memory-hotplug notifier and each time memory goes online or offline, rerun proc_root_kcore->size = get_kcore_size(...) - stop running get_kcore_size() within read_kcore(). I suspect that read_kcore() will not behave well if a memory hotplug operation happens concurrently. But that's a separate problem. (hopefully cc's some memory-hotplug people) Or we just leave /proc/kcore's st_size at zero. It's a pretty hopeless exercise trying to get this "right", as nobody can safely _use_ that size - it can be wrong as soon as the caller has read from it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/