From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755093Ab0EZM6W (ORCPT ); Wed, 26 May 2010 08:58:22 -0400 Received: from mail-fx0-f46.google.com ([209.85.161.46]:61669 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754673Ab0EZM6K (ORCPT ); Wed, 26 May 2010 08:58:10 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:x-enigmail-version:content-type :content-transfer-encoding; b=lTaEVDGbcCxjKbtw5SUXPudiPs00zVTY9r85ATiasVfcIjFyNikUQxpIBE1pQZaRrk YdTCrfy0TkTU5s+6ODPUM/zQEOQfDb3Ui6yJiImxdWPWr/ICD80xZ3wu+2JZC3buXS+P FUp0bgWNfPPjKPoVJllXRe6VybBDAGvIoTu1w= Message-ID: <4BFD1ADD.7020004@gmail.com> Date: Wed, 26 May 2010 14:58:05 +0200 From: Jiri Slaby User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; cs-CZ; rv:1.9.2.4) Gecko/20100522 SUSE/3.1rc1-2.1 Thunderbird/3.1 MIME-Version: 1.0 To: Andrew Morton CC: adobriyan@gmail.com, nhorman@tuxdriver.com, oleg@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 10/11] rlimits: implement prlimit64 syscall References: <1273514451-28894-1-git-send-email-jslaby@suse.cz> <1273514451-28894-10-git-send-email-jslaby@suse.cz> <20100513155630.9ca5ab16.akpm@linux-foundation.org> In-Reply-To: <20100513155630.9ca5ab16.akpm@linux-foundation.org> X-Enigmail-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/14/2010 12:56 AM, Andrew Morton wrote: > On Mon, 10 May 2010 20:00:50 +0200 > Jiri Slaby wrote: > >> This patch adds the code to support the sys_prlimit64 syscall which >> modifies-and-returns the rlim values of a selected process >> atomically. The first parameter, pid, being 0 means current process. >> >> Unlike the current implementation, it is a generic interface, >> architecture indepentent so that we needn't handle compat stuff >> anymore. In the future, after glibc start to use this we can deprecate >> sys_setrlimit and sys_getrlimit in favor to clean up the code finally. >> >> It also adds a possibility of changing limits of other processes. We >> check the user's permissions to do that and if it succeeds, the new >> limits are propagated online. This is good for large scale >> applications such as SAP or databases where administrators need to >> change limits time by time (e.g. on crashes increase core size). And >> it is unacceptable to restart the service. >> >> For safety, all rlim users now either use accessors or doesn't need >> them due to >> - locking >> - the fact a process was just forked and nobody else knows about it >> yet (and nobody can't thus read/write limits) >> hence it is safe to modify limits now. >> >> The limitation is that we currently stay at ulong internal >> representation. So we use the rlim64_is_infinity check where we >> compare to ULONG_MAX on 32-bit which is the maximum value there. >> >> And since internally we hold limits in struct rlimit, we introduce >> converters used before and after do_prlimit call in sys_prlimit64. >> > > Is this worth all the new code and the increase in locking dependencies > which I think is there? Sorry, for the late reply, I was busy with other things. Both tasklist_lock -> (task_struct->sighand->siglock) tasklist_lock -> (task_struct->alloc_lock) are OK, since both dependencies already exist in the kernel. This should have been in the changelogs, yes! > This could all be done in userspace, couldn't it? Write a little library > which clones a thread then waits for someone to send it a > change-your-rlimits message. Write a little tool to send those > messages and voila. Sorry, I'm not sure I understand this. Could you shed some light on what will run in the new thread? A code such as: main() { if (!clone()) exec("something"); while (wait_for_message(&m)) { setrlimit(m); sleep(); } } won't obviously work. Could you change it so it reflects your idea or explain what I'm missing? thanks, -- js