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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 CFDB7C282D8 for ; Wed, 30 Jan 2019 12:15:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD2AF20882 for ; Wed, 30 Jan 2019 12:15:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730716AbfA3MPa (ORCPT ); Wed, 30 Jan 2019 07:15:30 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:46878 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725768AbfA3MPa (ORCPT ); Wed, 30 Jan 2019 07:15:30 -0500 Received: from [2a01:598:b890:92b7:fc90:b8ff:fed0:1fb6] (helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1goom4-0006vD-T4; Wed, 30 Jan 2019 13:15:25 +0100 Date: Wed, 30 Jan 2019 13:15:18 +0100 (CET) From: Thomas Gleixner To: Heiko Carstens cc: Sebastian Sewior , Peter Zijlstra , Ingo Molnar , Martin Schwidefsky , LKML , linux-s390@vger.kernel.org, Stefan Liebler Subject: Re: WARN_ON_ONCE(!new_owner) within wake_futex_pi() triggered In-Reply-To: <20190130094913.GC5299@osiris> Message-ID: References: <20190128135804.GB28878@hirez.programming.kicks-ass.net> <20190129090108.GA26906@osiris> <20190129102409.GB26906@osiris> <20190129103557.GF28485@hirez.programming.kicks-ass.net> <20190129132303.GE26906@osiris> <20190129151058.GG26906@osiris> <20190129171653.ycl64psq2liy5o5c@linutronix.de> <20190130094913.GC5299@osiris> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Jan 2019, Heiko Carstens wrote: > On Tue, Jan 29, 2019 at 06:16:53PM +0100, Sebastian Sewior wrote: > > if (unlikely(p->flags & PF_KTHREAD)) { > > put_task_struct(p); > > Last lines of the trace with your additional patch (full log attached): > > <...>-50539 [003] .... 2376.398223: sys_futex -> 0x0 > <...>-50539 [003] .... 2376.398223: sys_futex(uaddr: 3ffb7700208, op: 6, val: 1, utime: 0, uaddr2: 3, val3: 0) > <...>-50539 [003] .... 2376.398225: attach_to_pi_owner: Missing pid 50734 > <...>-50539 [003] .... 2376.398226: handle_exit_race: uval2 vs uval 8000c62e vs 8000c62e (-1) So the user space value is: 8000c62e. FUTEX_WAITER bit is set and the owner of the futex is PID 50734, which exited long time ago: <...>-50734 [000] .... 2376.394936: sched_process_exit: comm=ld64.so.1 pid=50734 prio=120 But at least from the kernel view 50734 has released it last: <...>-50734 [000] .... 2376.394930: sys_futex(uaddr: 3ffb7700208, op: 7, val: 3ff00000007, utime: 3ffb3ef8910, uaddr2: 3ffb3ef8910, val3: 3ffc0afe987) <...>-50539 [003] .... 2376.398223: sys_futex(uaddr: 3ffb7700208, op: 6, val: 1, utime: 0, uaddr2: 3, val3: 0) Now, if it would have acquired it in userspace again before exiting, then the robust list exit code should have set the OWNER_DIED bit as well, but that's not set.... debug patch for the robust list exit handling below. Thanks, tglx 8<----------------- --- a/kernel/futex.c +++ b/kernel/futex.c @@ -3440,10 +3440,13 @@ static int handle_futex_death(u32 __user { u32 uval, uninitialized_var(nval), mval; + trace_printk("uaddr: %lx pi: %d\n", (unsigned long) uaddr, pi); retry: if (get_user(uval, uaddr)) return -1; + trace_printk("uaddr: %lx uval: %08x\n", (unsigned long) uaddr, uval); + if ((uval & FUTEX_TID_MASK) == task_pid_vnr(curr)) { /* * Ok, this dying thread is truly holding a futex @@ -3480,6 +3483,7 @@ static int handle_futex_death(u32 __user if (!pi && (uval & FUTEX_WAITERS)) futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY); } + trace_printk("uaddr: %lx success\n", (unsigned long) uaddr); return 0; }