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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 A5D3FC433DB for ; Fri, 5 Mar 2021 17:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 78591650A3 for ; Fri, 5 Mar 2021 17:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229576AbhCER44 (ORCPT ); Fri, 5 Mar 2021 12:56:56 -0500 Received: from out01.mta.xmission.com ([166.70.13.231]:50894 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229637AbhCER4t (ORCPT ); Fri, 5 Mar 2021 12:56:49 -0500 Received: from in02.mta.xmission.com ([166.70.13.52]) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lIEgu-004e9i-VG; Fri, 05 Mar 2021 10:56:45 -0700 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=fess.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1lIEgt-004li8-IX; Fri, 05 Mar 2021 10:56:44 -0700 From: ebiederm@xmission.com (Eric W. Biederman) To: Alexey Gladkov Cc: kernel test robot , 0day robot , LKML , lkp@lists.01.org, ying.huang@intel.com, feng.tang@intel.com, zhengjun.xing@intel.com, io-uring@vger.kernel.org, Kernel Hardening , Linux Containers , linux-mm@kvack.org, Andrew Morton , Christian Brauner , Jann Horn , Jens Axboe , Kees Cook , Linus Torvalds , Oleg Nesterov References: <20210224051845.GB6114@xsang-OptiPlex-9020> <20210224183828.j6uut6sholeo2fzh@example.org> <20210225203657.mjhaqnj5vszna5xw@example.org> Date: Fri, 05 Mar 2021 11:56:44 -0600 In-Reply-To: <20210225203657.mjhaqnj5vszna5xw@example.org> (Alexey Gladkov's message of "Thu, 25 Feb 2021 21:36:57 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1lIEgt-004li8-IX;;;mid=;;;hst=in02.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1+QpJmPwGjQCYsOz8d21ibu8x9BhUmL7YA= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: d28296d248: stress-ng.sigsegv.ops_per_sec -82.7% regression X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org Alexey Gladkov writes: > On Wed, Feb 24, 2021 at 12:50:21PM -0600, Eric W. Biederman wrote: >> Alexey Gladkov writes: >> >> > On Wed, Feb 24, 2021 at 10:54:17AM -0600, Eric W. Biederman wrote: >> >> kernel test robot writes: >> >> >> >> > Greeting, >> >> > >> >> > FYI, we noticed a -82.7% regression of stress-ng.sigsegv.ops_per_sec due to commit: >> >> > >> >> > >> >> > commit: d28296d2484fa11e94dff65e93eb25802a443d47 ("[PATCH v7 5/7] Reimplement RLIMIT_SIGPENDING on top of ucounts") >> >> > url: https://github.com/0day-ci/linux/commits/Alexey-Gladkov/Count-rlimits-in-each-user-namespace/20210222-175836 >> >> > base: https://git.kernel.org/cgit/linux/kernel/git/shuah/linux-kselftest.git next >> >> > >> >> > in testcase: stress-ng >> >> > on test machine: 48 threads Intel(R) Xeon(R) CPU E5-2697 v2 @ 2.70GHz with 112G memory >> >> > with following parameters: >> >> > >> >> > nr_threads: 100% >> >> > disk: 1HDD >> >> > testtime: 60s >> >> > class: interrupt >> >> > test: sigsegv >> >> > cpufreq_governor: performance >> >> > ucode: 0x42e >> >> > >> >> > >> >> > In addition to that, the commit also has significant impact on the >> >> > following tests: >> >> >> >> Thank you. Now we have a sense of where we need to test the performance >> >> of these changes carefully. >> > >> > One of the reasons for this is that I rolled back the patch that changed >> > the ucounts.count type to atomic_t. Now get_ucounts() is forced to use a >> > spin_lock to increase the reference count. >> >> Which given the hickups with getting a working version seems justified. >> >> Now we can add incremental patches on top to improve the performance. > > I'm not sure that get_ucounts() should be used in __sigqueue_alloc() [1]. > I tried removing it and running KASAN tests that were failing before. So > far, I have not found any problems. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/legion/linux.git/tree/kernel/signal.c?h=patchset/per-userspace-rlimit/v7.1&id=2d4a2e2be7db42c95acb98abfc2a9b370ddd0604#n428 Hmm. The code you posted still seems to include the get_ucounts. I like the idea of not needing to increment and decrement the ucount reference count every time a signal is sent, unfortunately there is a problem. The way we have implemented setresuid allows different threads in a threaded application to have different cred->user values. That is actually an extension of what posix supports and pthreads will keep the creds of a process in sync. Still I recall looking into this a few years ago and there were a few applications that take advantage of the linux behavior. In principle I think it is possible to hold a ucount reference in somewhere such as task->signal. In practice there are enough complicating factors I don't immediately see how to implement that. If the creds were stored in signal_struct instead of in task_struct we could simply move the sigpending counts in set_user, when the uid of a process changed. With the current state I don't know how to pick which is the real user. Eric