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=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 7CAE0C04FF3 for ; Fri, 21 May 2021 21:32:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E351613EE for ; Fri, 21 May 2021 21:32:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229550AbhEUVdp (ORCPT ); Fri, 21 May 2021 17:33:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229455AbhEUVdo (ORCPT ); Fri, 21 May 2021 17:33:44 -0400 Received: from mail-lf1-x130.google.com (mail-lf1-x130.google.com [IPv6:2a00:1450:4864:20::130]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE24BC061574 for ; Fri, 21 May 2021 14:32:20 -0700 (PDT) Received: by mail-lf1-x130.google.com with SMTP id a2so31657075lfc.9 for ; Fri, 21 May 2021 14:32:20 -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=r6vYR27HmzkzaqUZHwr4SiLt+czaPdhvvjAoc9a/8f4=; b=kbkZg3A0VW7YNL2AQdeZyjdjLFnKr0r5zNtON5zCs4W0SEs88Zb2w1stFkF4DAEKAv Xqt0m6CJLrU3EAR8lmuqG4s6wDsRaKPk4KLUcL47gCc/DrX5JfdDT42hPyurrI4foj61 B1JBSHMmHKbNIAanRxLZhpKZHXMmunxC6R7x+q5/SveC27YeODeQtGFuBYFTu/4JASLK /00mtD3rsIxST/xDhPx7jEA3Xoo1WrUpzeppSxzsTiSUYWJ8/Rk26w+bDG/CqASNqWYh 8644/xTDuxNQ80EZC2CoFwAfq18AquNHU/VySzNB4KObSyjI/JLsdywwn/UPSr6TEHPS LFGw== 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=r6vYR27HmzkzaqUZHwr4SiLt+czaPdhvvjAoc9a/8f4=; b=fav0wVv03drhJdjI38AS66ejKCn1qoEMlSi1Ax8lyCBSkIMTUivzXSwJuM2k7PYTmd rc+w5/kOIx91k0WQa0sewy92j9om9s23a6qqZfHPogxI+nwxLYawfK1aR5JFSb+cuS9u ClKp2kQc7wkm0R+rms6lFE1hp/j3uoYy5zpS1H15nlcyfgvzw3PemOMCtbwan7GcZGn8 CISm7IurLcAsTKSdTm0871WWBB1vngkgu4x+O5avgO2lFE5iDbxukZSI46w2jD3sU38G brjBWj9K0eh4axBb6yZySl8plrTge6LNkBz8Gqgqrrm94mKo/rBzhincR4gPJIR24MKb lI0w== X-Gm-Message-State: AOAM530fVVECEHvjPIsXVNT3iW5naTUt4UJsvfTogsT7BQmjwdAL8cQe 0rV3C+yY8QB+GB/OH0qINSM7gyOwsDqDhkYTCBqIjg== X-Google-Smtp-Source: ABdhPJwSS+3an+3n51uDLplzTHkpoN8PirrQ2vSH+OePXCfPOPzKmZC7X/nzbIlK+CqvlbDRj+Um0SQc2E8JUH/vu7E= X-Received: by 2002:ac2:44a2:: with SMTP id c2mr3549286lfm.74.1621632739009; Fri, 21 May 2021 14:32:19 -0700 (PDT) MIME-Version: 1.0 References: <20210520183614.1227046-1-posk@google.com> <20210520183614.1227046-5-posk@google.com> In-Reply-To: From: Jann Horn Date: Fri, 21 May 2021 23:31:52 +0200 Message-ID: Subject: Re: [RFC PATCH v0.1 4/9] sched/umcg: implement core UMCG API To: Andrei Vagin Cc: Peter Oskolkov , 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 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?