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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7E450C2D0F4 for ; Wed, 8 Apr 2020 20:17:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F20B206C0 for ; Wed, 8 Apr 2020 20:17:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="OorNDeym" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729171AbgDHURm (ORCPT ); Wed, 8 Apr 2020 16:17:42 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:20382 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726891AbgDHURl (ORCPT ); Wed, 8 Apr 2020 16:17:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586377060; 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: in-reply-to:in-reply-to:references:references; bh=lvTUjClSIk6Xg1FhK+FIzfVynQfhbiCCXnBY/h7tDyw=; b=OorNDeymrqxa+0POQML7+SAJ0nnCIsqxIvc9apqIpUXVMv3Ol2tULNi7JpoZeFqV8TKMf3 Hc0BTNsh05hfnTLYkjzpxYnyGNKGaCF5Ajl31F0q83RI7anvxjSFqsVMSKutffXXV5Q1p8 eB0wbhsx2HN9kRQE2vAu3C8HXvgdUrA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-304-E3xDWTSeOzGLQTAKTRE2-w-1; Wed, 08 Apr 2020 16:17:38 -0400 X-MC-Unique: E3xDWTSeOzGLQTAKTRE2-w-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 7E5571084426; Wed, 8 Apr 2020 20:17:37 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.143]) by smtp.corp.redhat.com (Postfix) with SMTP id 1762460BFB; Wed, 8 Apr 2020 20:17:35 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 8 Apr 2020 22:17:37 +0200 (CEST) Date: Wed, 8 Apr 2020 22:17:35 +0200 From: Oleg Nesterov To: Jens Axboe Cc: io-uring@vger.kernel.org, viro@zeniv.linux.org.uk, Peter Zijlstra Subject: Re: [PATCH 4/4] io_uring: flush task work before waiting for ring exit Message-ID: <20200408201734.GA21347@redhat.com> References: <20200407160258.933-1-axboe@kernel.dk> <20200407160258.933-5-axboe@kernel.dk> <20200407162405.GA9655@redhat.com> <20200407163816.GB9655@redhat.com> <4b70317a-d12a-6c29-1d7f-1394527f9676@kernel.dk> <20200408184049.GA25918@redhat.com> <6d320b43-254d-2d42-cbad-d323f1532e65@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6d320b43-254d-2d42-cbad-d323f1532e65@kernel.dk> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 04/08, Jens Axboe wrote: > > Here's some more data. I added a WARN_ON_ONCE() for task->flags & > PF_EXITING on task_work_add() success, and it triggers with the > following backtrace: ... > which means that we've successfully added the task_work while the > process is exiting. but this is fine, task_work_add(task) can succeed if task->flags & EXITING. task_work_add(task, work) should only fail if this "task" has already passed exit_task_work(). Because if this task has already passed exit_task_work(), nothing else can flush this work and call work->func(). Oleg.