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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3998C001B0 for ; Fri, 7 Jul 2023 17:57:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231929AbjGGR5z (ORCPT ); Fri, 7 Jul 2023 13:57:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232245AbjGGR5w (ORCPT ); Fri, 7 Jul 2023 13:57:52 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7F1C170F for ; Fri, 7 Jul 2023 10:57:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688752630; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=jJ/fuG3K5KSAUU81uckV1RdmVyNYdH1eHdjrqxK1TTw=; b=IKvCHJQ7vCaEh+Erd1iLxQePMvoK9KLZaPaLaQVQhUFVZHOKezTxZa2cJUb5tNITbZ0TKI RezQ6WJ0D5fnxR09Z3pzhglshKptcspMEOLNk3FjovfbFiXjaimtONI8enP5TruyMiNfF0 mxhK+OyQ3LSTkXoBvjGEoWcTLGxSFh0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-510-Py09K79eOiubwylG_AYfpw-1; Fri, 07 Jul 2023 13:57:03 -0400 X-MC-Unique: Py09K79eOiubwylG_AYfpw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 0A895381D4D8; Fri, 7 Jul 2023 17:57:03 +0000 (UTC) Received: from [10.22.34.12] (unknown [10.22.34.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6E38A4087C6A; Fri, 7 Jul 2023 17:57:02 +0000 (UTC) Message-ID: Date: Fri, 7 Jul 2023 13:57:02 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH] refscale: Fix use of uninitalized wait_queue_head_t Content-Language: en-US To: paulmck@kernel.org Cc: Davidlohr Bueso , Josh Triplett , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Boqun Feng , Zqiang , rcu@vger.kernel.org, linux-kernel@vger.kernel.org References: <20230707000117.2371697-1-longman@redhat.com> <8b827d44-b19b-4eb2-8860-f419cc61084e@paulmck-laptop> From: Waiman Long In-Reply-To: <8b827d44-b19b-4eb2-8860-f419cc61084e@paulmck-laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/7/23 12:16, Paul E. McKenney wrote: > On Fri, Jul 07, 2023 at 10:56:51AM -0400, Waiman Long wrote: >> On 7/7/23 10:07, Davidlohr Bueso wrote: >>> On Thu, 06 Jul 2023, Waiman Long wrote: >>> >>>> It was found that running the refscale test might sometimes crash the >>>> kernel with the following error: >>>> >>>> [ 8569.952896] BUG: unable to handle page fault for address: >>>> ffffffffffffffe8 >>>> [ 8569.952900] #PF: supervisor read access in kernel mode >>>> [ 8569.952902] #PF: error_code(0x0000) - not-present page >>>> [ 8569.952904] PGD c4b048067 P4D c4b049067 PUD c4b04b067 PMD 0 >>>> [ 8569.952910] Oops: 0000 [#1] PREEMPT_RT SMP NOPTI >>>> [ 8569.952916] Hardware name: Dell Inc. PowerEdge R750/0WMWCR, BIOS >>>> 1.2.4 05/28/2021 >>>> [ 8569.952917] RIP: 0010:prepare_to_wait_event+0x101/0x190 >>>>  : >>>> [ 8569.952940] Call Trace: >>>> [ 8569.952941]  >>>> [ 8569.952944]  ref_scale_reader+0x380/0x4a0 [refscale] >>>> [ 8569.952959]  kthread+0x10e/0x130 >>>> [ 8569.952966]  ret_from_fork+0x1f/0x30 >>>> [ 8569.952973]  >>>> >>>> This is likely caused by the fact that init_waitqueue_head() is called >>>> after the ref_scale_reader kthread is created. So the kthread may try >>>> to use the waitqueue head before it is properly initialized. Fix this >>>> by initializing the waitqueue head first before kthread creation. >>>> >>>> Fixes: 653ed64b01dc ("refperf: Add a test to measure performance of >>>> read-side synchronization") >>>> Signed-off-by: Waiman Long >>> Strange this wasn't reported sooner. >> Red Hat does have a pretty large QE organization that run all sort of tests >> include this one pretty frequently. The race window is pretty small, but >> they did hit this once in a while. > I do run this fairly frequently, but haven't managed to hit it. > > Good show on making it happen, and looking forward to the updated patch! v2 sent with a bit more explanation text in the commit log. Cheers, Longman