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=-11.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 E370EC4727D for ; Thu, 24 Sep 2020 16:21:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A22552396D for ; Thu, 24 Sep 2020 16:21:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726522AbgIXQVa (ORCPT ); Thu, 24 Sep 2020 12:21:30 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:35348 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbgIXQVa (ORCPT ); Thu, 24 Sep 2020 12:21:30 -0400 Received: from ip5f5af089.dynamic.kabel-deutschland.de ([95.90.240.137] helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.86_2) (envelope-from ) id 1kLTzr-00031R-6I; Thu, 24 Sep 2020 16:21:27 +0000 Date: Thu, 24 Sep 2020 18:21:26 +0200 From: Christian Brauner To: Naresh Kamboju Cc: "open list:KERNEL SELFTEST FRAMEWORK" , linux-api@vger.kernel.org, open list , Christian Brauner , Kees Cook , "Peter Zijlstra (Intel)" , Ingo Molnar , Thomas Gleixner , Oleg Nesterov , "Eric W. Biederman" , Sargun Dhillon , Aleksa Sarai , Josh Triplett , Jens Axboe , Shuah Khan , lkft-triage@lists.linaro.org Subject: Re: selftests: pidfd: pidfd_wait hangs on linux next kernel on all devices Message-ID: <20200924162126.mbthwz32w7rba7oe@wittgenstein> References: <20200924143317.getruzwu423g3o3e@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200924143317.getruzwu423g3o3e@wittgenstein> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Sep 24, 2020 at 04:33:17PM +0200, Christian Brauner wrote: > On Wed, Sep 23, 2020 at 07:52:05PM +0530, Naresh Kamboju wrote: > > selftests: pidfd: pidfd_wait hangs on linux next kernel on x86_64, > > i386 and arm64 Juno-r2 > > These devices are using NFS mounted rootfs. > > I have tested pidfd testcases independently and all test PASS. > > > > The Hang or exit from test run noticed when run by run_kselftest.sh > > > > pidfd_wait.c:208:wait_nonblock:Expected sys_waitid(P_PIDFD, pidfd, > > &info, WSTOPPED, NULL) (-1) == 0 (0) > > wait_nonblock: Test terminated by assertion > > > > metadata: > > git branch: master > > git repo: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git > > git commit: e64997027d5f171148687e58b78c8b3c869a6158 > > git describe: next-20200922 > > make_kernelversion: 5.9.0-rc6 > > kernel-config: > > http://snapshots.linaro.org/openembedded/lkft/lkft/sumo/intel-core2-32/lkft/linux-next/865/config > > > > Reported-by: Naresh Kamboju > > Thanks for reproting this. I'm taking a look now! Ok, this is a simple race in the selftests, that I overlooked and which is more likely to hit when there's a lot of processes running on the system. Basically the child process hasn't SIGSTOPed itself yet but the parent is already calling waitid() on a O_NONBLOCK pidfd. Since it doesn't find a WSTOPPED process it returns -EAGAIN correctly. The fix for this is to move the line where we're removing the O_NONBLOCK property from the fd before the waitid() WSTOPPED call so we hang until the child becomes stopped. So I believe the fix is: diff --git a/tools/testing/selftests/pidfd/pidfd_wait.c b/tools/testing/selftests/pidfd/pidfd_wait.c index 4063d6f31fa4..be2943f072f6 100644 --- a/tools/testing/selftests/pidfd/pidfd_wait.c +++ b/tools/testing/selftests/pidfd/pidfd_wait.c @@ -205,6 +205,8 @@ TEST(wait_nonblock) ret = sys_waitid(P_PIDFD, pidfd, &info, WEXITED | WNOHANG, NULL); ASSERT_EQ(ret, 0); + ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 0); + ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WSTOPPED, NULL), 0); ASSERT_EQ(info.si_signo, SIGCHLD); ASSERT_EQ(info.si_code, CLD_STOPPED); @@ -212,8 +214,6 @@ TEST(wait_nonblock) ASSERT_EQ(sys_pidfd_send_signal(pidfd, SIGCONT, NULL, 0), 0); - ASSERT_EQ(fcntl(pidfd, F_SETFL, (flags & ~O_NONBLOCK)), 0); - ASSERT_EQ(sys_waitid(P_PIDFD, pidfd, &info, WEXITED, NULL), 0); ASSERT_EQ(info.si_signo, SIGCHLD); ASSERT_EQ(info.si_code, CLD_EXITED); Christian