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=-10.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 BE760C433E0 for ; Fri, 8 Jan 2021 13:42:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86723239ED for ; Fri, 8 Jan 2021 13:42:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727790AbhAHNm2 (ORCPT ); Fri, 8 Jan 2021 08:42:28 -0500 Received: from mx2.suse.de ([195.135.220.15]:36552 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726784AbhAHNm1 (ORCPT ); Fri, 8 Jan 2021 08:42:27 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1610113300; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=vIiuK/wpdb0akmqoEm2pC/CdRsjvf61e0Abm1+FwZg0=; b=V1k3ZtkTeyNdUza0KvYJ6mwSqO20PfusCDmin8X8y3D6HmNEuKlnaZj59khmKMDi0v6OSD jSXg8gXcZIG08uSeS5RhUqo4pTXDKRmgos+HXO/821GoeC8cHgSjLWxEo/MrLOy1ZiUx09 gkaXNkhczn73l5EOricoAQUoN+2ZuWE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id D1FDAAD11; Fri, 8 Jan 2021 13:41:40 +0000 (UTC) Date: Fri, 8 Jan 2021 14:41:40 +0100 From: Michal Hocko To: Milan Broz Cc: linux-mm@kvack.org, Linux Kernel Mailing List , Mikulas Patocka Subject: Re: Very slow unlockall() Message-ID: <20210108134140.GA9883@dhcp22.suse.cz> References: <70885d37-62b7-748b-29df-9e94f3291736@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <70885d37-62b7-748b-29df-9e94f3291736@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 06-01-21 16:20:15, Milan Broz wrote: > Hi, > > we use mlockall(MCL_CURRENT | MCL_FUTURE) / munlockall() in cryptsetup code > and someone tried to use it with hardened memory allocator library. > > Execution time was increased to extreme (minutes) and as we found, the problem > is in munlockall(). > > Here is a plain reproducer for the core without any external code - it takes > unlocking on Fedora rawhide kernel more than 30 seconds! > I can reproduce it on 5.10 kernels and Linus' git. > > The reproducer below tries to mmap large amount memory with PROT_NONE (later never used). > The real code of course does something more useful but the problem is the same. > > #include > #include > #include > #include > > int main (int argc, char *argv[]) > { > void *p = mmap(NULL, 1UL << 41, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); > > if (p == MAP_FAILED) return 1; > > if (mlockall(MCL_CURRENT | MCL_FUTURE)) return 1; > printf("locked\n"); > > if (munlockall()) return 1; > printf("unlocked\n"); > > return 0; > } > > In traceback I see that time is spent in munlock_vma_pages_range. > > [ 2962.006813] Call Trace: > [ 2962.006814] ? munlock_vma_pages_range+0xe7/0x4b0 > [ 2962.006814] ? vma_merge+0xf3/0x3c0 > [ 2962.006815] ? mlock_fixup+0x111/0x190 > [ 2962.006815] ? apply_mlockall_flags+0xa7/0x110 > [ 2962.006816] ? __do_sys_munlockall+0x2e/0x60 > [ 2962.006816] ? do_syscall_64+0x33/0x40 > ... > > Or with perf, I see > > # Overhead Command Shared Object Symbol > # ........ ....... ................. ..................................... > # > 48.18% lock [kernel.kallsyms] [k] lock_is_held_type > 11.67% lock [kernel.kallsyms] [k] ___might_sleep > 10.65% lock [kernel.kallsyms] [k] follow_page_mask > 9.17% lock [kernel.kallsyms] [k] debug_lockdep_rcu_enabled > 6.73% lock [kernel.kallsyms] [k] munlock_vma_pages_range > ... > > > Could please anyone check what's wrong here with the memory locking code? > Running it on my notebook I can effectively DoS the system :) > > Original report is https://gitlab.com/cryptsetup/cryptsetup/-/issues/617 > but this is apparently a kernel issue, just amplified by usage of munlockall(). Which kernel version do you see this with? Have older releases worked better? -- Michal Hocko SUSE Labs