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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=no 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 5341AC4321A for ; Sat, 29 Jun 2019 01:49:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 245EE214AF for ; Sat, 29 Jun 2019 01:49:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726907AbfF2BtH (ORCPT ); Fri, 28 Jun 2019 21:49:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:51454 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726682AbfF2BtG (ORCPT ); Fri, 28 Jun 2019 21:49:06 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3B5B12083B; Sat, 29 Jun 2019 01:49:05 +0000 (UTC) Date: Fri, 28 Jun 2019 21:49:03 -0400 From: Steven Rostedt To: Sebastian Andrzej Siewior Cc: minyard@acm.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , tglx@linutronix.de, Corey Minyard Subject: Re: [PATCH RT v2] Fix a lockup in wait_for_completion() and friends Message-ID: <20190628214903.6f92a9ea@oasis.local.home> In-Reply-To: <20190510103318.6cieoifz27eph4n5@linutronix.de> References: <20190509193320.21105-1-minyard@acm.org> <20190510103318.6cieoifz27eph4n5@linutronix.de> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 10 May 2019 12:33:18 +0200 Sebastian Andrzej Siewior wrote: > On 2019-05-09 14:33:20 [-0500], minyard@acm.org wrote: > > From: Corey Minyard > > > > The function call do_wait_for_common() has a race condition that > > can result in lockups waiting for completions. Adding the thread > > to (and removing the thread from) the wait queue for the completion > > is done outside the do loop in that function. However, if the thread > > is woken up, the swake_up_locked() function will delete the entry > > from the wait queue. If that happens and another thread sneaks > > in and decrements the done count in the completion to zero, the > > loop will go around again, but the thread will no longer be in the > > wait queue, so there is no way to wake it up. > > applied, thank you. > When I applied this patch to 4.19-rt, I get the following lock up: watchdog: BUG: soft lockup - CPU#2 stuck for 22s! [sh:745] Modules linked in: floppy i915 drm_kms_helper drm fb_sys_fops sysimgblt sysfillrect syscopyarea iosf_mbi i2c_algo_bit video CPU: 2 PID: 745 Comm: sh Not tainted 4.19.56-test-rt23+ #16 Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007 RIP: 0010:_raw_spin_unlock_irq+0x17/0x4d Code: 48 8b 12 0f ba e2 12 73 07 e8 f1 4a 92 ff 31 c0 5b 5d c3 66 66 66 66 90 55 48 89 e5 c6 07 00 e8 de 3d a3 ff fb bf 01 00 00 00 a7 27 9a ff 65 8b 05 c8 7f 93 7e 85 c0 74 1f a9 ff ff ff 7f 75 RSP: 0018:ffffc90000c8bbb8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 RAX: 0000000000000000 RBX: ffffc90000c8bd58 RCX: 0000000000000003 RDX: 0000000000000000 RSI: ffffffff8108ffab RDI: 0000000000000001 RBP: ffffc90000c8bbb8 R08: ffffffff816dcd76 R09: 0000000000020600 R10: 0000000000000400 R11: 0000001c0eef1808 R12: ffffc90000c8bbc8 R13: ffffc90000f13ca0 R14: ffff888074b2d7d8 R15: ffff8880789efe10 FS: 0000000000000000(0000) GS:ffff88807b300000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00000030662001b8 CR3: 00000000376ac000 CR4: 00000000000006e0 Call Trace: swake_up_all+0xa6/0xde __d_lookup_done+0x7c/0xc7 __d_add+0x44/0xf7 d_splice_alias+0x208/0x218 ext4_lookup+0x1a6/0x1c5 path_openat+0x63a/0xb15 ? preempt_latency_stop+0x25/0x27 do_filp_open+0x51/0xae ? trace_preempt_on+0xde/0xe7 ? rt_spin_unlock+0x13/0x24 ? __alloc_fd+0x145/0x155 do_sys_open+0x81/0x125 __x64_sys_open+0x21/0x23 do_syscall_64+0x5c/0x6e entry_SYSCALL_64_after_hwframe+0x49/0xbe I haven't really looked too much into it though. I ran out of time :-/ -- Steve