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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 63D00C4707A for ; Fri, 21 May 2021 22:03:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B67C611ED for ; Fri, 21 May 2021 22:03:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229543AbhEUWE6 (ORCPT ); Fri, 21 May 2021 18:04:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229472AbhEUWEz (ORCPT ); Fri, 21 May 2021 18:04:55 -0400 Received: from mail-lj1-x22c.google.com (mail-lj1-x22c.google.com [IPv6:2a00:1450:4864:20::22c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 20F84C0613CE for ; Fri, 21 May 2021 15:03:32 -0700 (PDT) Received: by mail-lj1-x22c.google.com with SMTP id t17so8948710ljd.9 for ; Fri, 21 May 2021 15:03:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=QlIMY15CpFScH+ksxa68jbEZt4sckreO5cTytM/uKyQ=; b=NcsSM/s4rzD7dlt+04clT1uj5dtUq5BhwFimvnhztIB6rQKNDP+rOxORZp7zivcDiB +adfZgxAxkfkXXTIkjUzTVCmhnbhpjOOKH5/yw/PQ5X/S4EkYqASi2W6yBYlqBTJPd2N UzXw9Pg8df34MaaYYHM2xkjZ6Wg+4MPwF0PqPgsUzEI1kLsT+C937e7gFzw7GO/pellR kmwHPOQxI6f20m+ryg58lE+B0x1PhdGa5R0m03/W6juP7HGsLCGzLUo+XoBQ1CypsgPv X2jfAWDHInGbYBeYbUE3Vl1bjkf2yO97SP2tEK2EVjGl21JBpTNFqFlVGlaUwnVtH/CB 4Ddg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=QlIMY15CpFScH+ksxa68jbEZt4sckreO5cTytM/uKyQ=; b=dsQfQyfSpItV4ps43KkLqkgPcxU4VjSYnQTjSOosx5i0kSbqJaWQeuv/i/CoJq12xF eCyrYjBzqZ0cz0RW9lb1jvYxK/W7lo5lJDVyZo3aL3J9mzS1qdLGrEzBSHuhRwxEmeIX bxk5DAHNERJRib0Ddovm5dMYcI6jC3+4q8FfjLvqu4RGZPhnIn2D8jGen6tcMnVcioCy VI94QleMf2KIHZA9l9QDXT3bnFXtw+YpLICjjEn7E4YypaRdthp8a8YKZBHw8jhVjgCA hbR9XJgHSbmcVxY59fqdxxrE2aH4I0VR98uykuvPtbUXWTm0fazlyaWlyojb/YYe6mv+ Sr6g== X-Gm-Message-State: AOAM532KxdM/jrYDf5WGO59o+QtpuewY/BOxU7vryHZ5exQbLZvY2s+/ WFK+Df0On9u/N4x42+hm0+LBsg7qwjQAoZxhhlz7xg== X-Google-Smtp-Source: ABdhPJw+0Qgixkebi05CmJcybmpLEK8eFm8/RcA/Uyc8tm1QpjZrtF09sMlvAAj4osycGZDCHoKp9ZCK05jucXh09ks= X-Received: by 2002:a2e:9c05:: with SMTP id s5mr7976368lji.208.1621634610156; Fri, 21 May 2021 15:03:30 -0700 (PDT) MIME-Version: 1.0 References: <20210520183614.1227046-1-posk@google.com> <20210520183614.1227046-5-posk@google.com> In-Reply-To: From: Peter Oskolkov Date: Fri, 21 May 2021 15:03:18 -0700 Message-ID: Subject: Re: [RFC PATCH v0.1 4/9] sched/umcg: implement core UMCG API To: Jann Horn Cc: Andrei Vagin , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , kernel list , Linux API , Paul Turner , Ben Segall , Peter Oskolkov , Joel Fernandes , Andrew Morton , Andrei Vagin , Jim Newsome Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 21, 2021 at 2:32 PM Jann Horn wrote: > > On Fri, May 21, 2021 at 9:09 PM Andrei Vagin wrote: > > On Thu, May 20, 2021 at 11:36:09AM -0700, Peter Oskolkov wrote: > > > @@ -67,7 +137,75 @@ SYSCALL_DEFINE4(umcg_register_task, u32, api_version, u32, flags, u32, group_id, > > > */ > > > SYSCALL_DEFINE1(umcg_unregister_task, u32, flags) > > > { > > > - return -ENOSYS; > > > + struct umcg_task_data *utd; > > > + int ret = -EINVAL; > > > + > > > + rcu_read_lock(); > > > + utd = rcu_dereference(current->umcg_task_data); > > > + > > > + if (!utd || flags) > > > + goto out; > > > + > > > + task_lock(current); > > > + rcu_assign_pointer(current->umcg_task_data, NULL); > > > + task_unlock(current); > > > + > > > + ret = 0; > > > + > > > +out: > > > + rcu_read_unlock(); > > > + if (!ret && utd) { > > > + synchronize_rcu(); > > > > synchronize_rcu is expensive. Do we really need to call it here? Can we > > use kfree_rcu? > > > > Where is task->umcg_task_data freed when a task is destroyed? > > or executed - the umcg stuff includes a userspace pointer, so it > probably shouldn't normally be kept around across execve? Ack - thanks for these and other comments. Please keep them coming. I'll address them in v0.2. Thanks, Peter