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=-2.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 1500AC433E6 for ; Sat, 16 Jan 2021 17:13:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B7A3122527 for ; Sat, 16 Jan 2021 17:13:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726780AbhAPRKl (ORCPT ); Sat, 16 Jan 2021 12:10:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728339AbhAPRKh (ORCPT ); Sat, 16 Jan 2021 12:10:37 -0500 Received: from mail-io1-xd2f.google.com (mail-io1-xd2f.google.com [IPv6:2607:f8b0:4864:20::d2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 78DD0C06135E for ; Sat, 16 Jan 2021 08:14:46 -0800 (PST) Received: by mail-io1-xd2f.google.com with SMTP id u17so24322807iow.1 for ; Sat, 16 Jan 2021 08:14:46 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ee2WNqGNvbcVmc69Zvx/j7MrYt0u8UOawahie9yb7f4=; b=PrEWV6kr1XyrHNJFa7YNo2pBPPiD6xd+D06HRc6JgcjkHQCjtIgjgCdupgOXBw0VCQ MwfAFgbIBlIbdPJihZgaOl+AHyMUnl6GXTexuiM8ebHb273mTFcIRGoHf5hyiTTZkFfN FGVul0vvzdOqWNzQXqkEvMIQ6VkchpudBr7XY+jnUp9V4IPP6K89Mo+2BOCLcSQUHggK +ju9AZTVZfpnZv/Jj6tQUvV4nGjSgzbGFDYpNdn7Z09vvjVa01cfZpHD1Oto6aSG/hrR eY3S4TvZXnkpLebWQwjozJ2gWcuPP0dHOt7p4ALn0aexDwN//6/EOJAGNyaIhE/97ZyH jWTQ== 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=ee2WNqGNvbcVmc69Zvx/j7MrYt0u8UOawahie9yb7f4=; b=QaZJ9gDLiK6JCLCk6CCT6izEV2tb9HHyMv5vdpQcZJw2EJJx1WsfNuvMmWLAhJO9Yf SUKIMBdlFLmfVfV+CcNlyWOMwocpZ4n0rHJ1sBo3X5s7vrxDPDtW79XVm/AYqyldggYr VdczKp58wRtLY9daLPQQXsqG5FjqDdWHxaMIf1qBGxQbL6vQUmbdptlGGbPV69I+C5qN V4BCkdMVr+BxRtx3ViODajo3ghD3Ll1XOOSTFlpjGggjIlOrxPv3ME3HD7ToTdSZ+DFy 7dyfarD4i0dNEx5inrN3FLVrCXyj/OeMww9pGYiiOkdI5FC9bGdCjDygAYGoNvqWKXcb 5W1Q== X-Gm-Message-State: AOAM532XThtc9bp5S9aavPLRx8RKeK5Qy2P0C5fIsFVjFdbPWFX5AdcV rvxvkMd2rupWgX4RfjLirrrZnoOa8/5TaMNfCa8= X-Google-Smtp-Source: ABdhPJzm7UAoZ7rktA+SBFMrZYGVB7ycmqTUR5CXM/0YBlIUw8ef92QJgNexLp0/sasANmsOealOtsSSPJprDFwyhmY= X-Received: by 2002:a5d:8c85:: with SMTP id g5mr12226334ion.154.1610813685872; Sat, 16 Jan 2021 08:14:45 -0800 (PST) MIME-Version: 1.0 References: <20210112144344.850850975@infradead.org> <20210112144843.849135905@infradead.org> In-Reply-To: From: Lai Jiangshan Date: Sun, 17 Jan 2021 00:14:34 +0800 Message-ID: Subject: Re: [PATCH 3/4] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU To: Peter Zijlstra Cc: Valentin Schneider , Ingo Molnar , Thomas Gleixner , LKML , Qian Cai , Vincent Donnefort , Dexuan Cui , "Paul E. McKenney" , Vincent Guittot , Steven Rostedt , Tejun Heo Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 16, 2021 at 11:16 PM Peter Zijlstra wrote: > > On Sat, Jan 16, 2021 at 10:45:04PM +0800, Lai Jiangshan wrote: > > On Sat, Jan 16, 2021 at 8:45 PM Peter Zijlstra wrote: > > > It is also the exact sequence normal per-cpu threads (smpboot) use to > > > preserve affinity. > > > > Other per-cpu threads normally do short-live works. wq's work can be > > lengthy, cpu-intensive, heavy-lock-acquiring or even call > > get_online_cpus() which might result in a deadlock with kthread_park(). > > kthread_park() is called by the migration thread running the > workqueue_online_cpu() callback. > > kthread_parkme() is called by the worker thread, after it completes a > work and has no locks held from that context. > > BP: AP: worker: cpus_write_lock() bringup_cpu() work_item_func() bringup_wait_for_ap get_online_cpus() kthread_park(worker)