From patchwork Fri Jun 11 16:41:55 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Hansen X-Patchwork-Id: 12316175 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=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED 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 5CB67C48BE0 for ; Fri, 11 Jun 2021 16:42:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 10B606100A for ; Fri, 11 Jun 2021 16:42:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10B606100A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A6B8F6B006C; Fri, 11 Jun 2021 12:42:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A43016B006E; Fri, 11 Jun 2021 12:42:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8BC966B0070; Fri, 11 Jun 2021 12:42:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0222.hostedemail.com [216.40.44.222]) by kanga.kvack.org (Postfix) with ESMTP id 5CC996B006C for ; Fri, 11 Jun 2021 12:42:04 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 02B1EBBDE for ; Fri, 11 Jun 2021 16:42:04 +0000 (UTC) X-FDA: 78242010168.04.4AF34D9 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by imf20.hostedemail.com (Postfix) with ESMTP id 82B9D54C for ; Fri, 11 Jun 2021 16:41:55 +0000 (UTC) IronPort-SDR: 8nE1fginkxwZH7nm5NerusdZTyOkL8YxDGqlGozLZphLKmsNgsANdJz1qG7VFjDrSeOayHdvCf 3LWg/aZvKBAw== X-IronPort-AV: E=McAfee;i="6200,9189,10012"; a="226987438" X-IronPort-AV: E=Sophos;i="5.83,265,1616482800"; d="scan'208";a="226987438" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jun 2021 09:41:58 -0700 IronPort-SDR: lUbd/cezG/WIoeYhLWfpKT7TAWTnR53Ta8JFebAxza+auFaTWefdJRvLcFLUEX09wp+JBQJF5w nHDtT76H4G8g== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.83,265,1616482800"; d="scan'208";a="420122331" Received: from viggo.jf.intel.com (HELO localhost.localdomain) ([10.54.77.144]) by orsmga002.jf.intel.com with ESMTP; 11 Jun 2021 09:41:56 -0700 Subject: [PATCH 1/4] selftests/vm/pkeys: Fix alloc_random_pkey() to make it really, really random To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org,Dave Hansen ,tglx@linutronix.de,linuxram@us.ibm.com,sandipan@linux.ibm.com,akpm@linux-foundation.org,fweimer@redhat.com,desnesn@linux.vnet.ibm.com,mingo@kernel.org,bauerman@linux.ibm.com,aneesh.kumar@linux.ibm.com,mpe@ellerman.id.au,mhocko@kernel.org,msuchanek@suse.de,shuah@kernel.org,x86@kernel.org From: Dave Hansen Date: Fri, 11 Jun 2021 09:41:55 -0700 References: <20210611164153.91B76FB8@viggo.jf.intel.com> In-Reply-To: <20210611164153.91B76FB8@viggo.jf.intel.com> Message-Id: <20210611164155.192D00FF@viggo.jf.intel.com> Authentication-Results: imf20.hostedemail.com; dkim=none; spf=none (imf20.hostedemail.com: domain of dave.hansen@linux.intel.com has no SPF policy when checking 192.55.52.88) smtp.mailfrom=dave.hansen@linux.intel.com; dmarc=fail reason="No valid SPF, No valid DKIM" header.from=intel.com (policy=none) X-Stat-Signature: aaph9frwa87bu1z8rdhqkix7og8u4mhc X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 82B9D54C X-HE-Tag: 1623429715-3303 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Dave Hansen The "random" pkey allocation code currently does the good old: srand((unsigned int)time(NULL)); *But*, it unfortunately does this on every random pkey allocation. There may be thousands of these a second. time() has a one second resolution. So, each time alloc_random_pkey() is called, the PRNG is *RESET* to time(). This is nasty. Normally, if you do: srand(); foo = rand(); bar = rand(); You'll be quite guaranteed that 'foo' and 'bar' are different. But, if you do: srand(1); foo = rand(); srand(1); bar = rand(); You are quite guaranteed that 'foo' and 'bar' are the *SAME*. The recent "fix" effectively forced the test case to use the same "random" pkey for the whole test, unless the test run crossed a second boundary. Only run srand() once at program startup. This explains some very odd and persistent test failures I've been seeing. Fixes: 6e373263ce07 ("selftests/vm/pkeys: fix alloc_random_pkey() to make it really random") Signed-off-by: Dave Hansen Signed-off-by: Thomas Gleixner Cc: Ram Pai Cc: Sandipan Das Cc: Andrew Morton Cc: Florian Weimer Cc: "Desnes A. Nunes do Rosario" Cc: Ingo Molnar Cc: Thiago Jung Bauermann Cc: "Aneesh Kumar K.V" Cc: Michael Ellerman Cc: Michal Hocko Cc: Michal Suchanek Cc: Shuah Khan Cc: x86@kernel.org --- b/tools/testing/selftests/vm/protection_keys.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff -puN tools/testing/selftests/vm/protection_keys.c~selftests_vm_pkeys_Fix_alloc_random_pkey_to_make_it_really_really_random-1 tools/testing/selftests/vm/protection_keys.c --- a/tools/testing/selftests/vm/protection_keys.c~selftests_vm_pkeys_Fix_alloc_random_pkey_to_make_it_really_really_random-1 2021-06-11 09:41:31.385468066 -0700 +++ b/tools/testing/selftests/vm/protection_keys.c 2021-06-11 09:41:31.389468066 -0700 @@ -561,7 +561,6 @@ int alloc_random_pkey(void) int nr_alloced = 0; int random_index; memset(alloced_pkeys, 0, sizeof(alloced_pkeys)); - srand((unsigned int)time(NULL)); /* allocate every possible key and make a note of which ones we got */ max_nr_pkey_allocs = NR_PKEYS; @@ -1552,6 +1551,8 @@ int main(void) int nr_iterations = 22; int pkeys_supported = is_pkeys_supported(); + srand((unsigned int)time(NULL)); + setup_handlers(); printf("has pkeys: %d\n", pkeys_supported);