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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B2CAC433F5 for ; Mon, 1 Nov 2021 21:01:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA038610FC for ; Mon, 1 Nov 2021 21:01:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230296AbhKAVEJ (ORCPT ); Mon, 1 Nov 2021 17:04:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60706 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229501AbhKAVEG (ORCPT ); Mon, 1 Nov 2021 17:04:06 -0400 Received: from mail-lj1-x232.google.com (mail-lj1-x232.google.com [IPv6:2a00:1450:4864:20::232]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 39354C061714 for ; Mon, 1 Nov 2021 14:01:32 -0700 (PDT) Received: by mail-lj1-x232.google.com with SMTP id 1so25522440ljv.2 for ; Mon, 01 Nov 2021 14:01:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=gDtjUUVqt9XgvCkiF8UV0KJSKzhaYXkrtMs8KFbWrS8=; b=hPlSVyiXX/EZBkKOxYuDez+7b2s9EUBNHI/pp/DKfeLZli1omRWqcAGTxbn/5TAS8z NJPd8Bgj9Ptqffd6oVyG6WnhPvGFs4ImDDyBqKaaOvb0rdUVSWRJnrEtrdVKms2suzuB rz0fLtDEJjfR5SXuE0F5Ta++vm2izjISjipIQ= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=gDtjUUVqt9XgvCkiF8UV0KJSKzhaYXkrtMs8KFbWrS8=; b=NuS3ei/EKrB4gNOwWy1JmBaCd5+nL9LW612HT24YP5B+rgvSihiq38RmescVwFKr0z +gJC9+oqAo1JjmxHxoSz+QDEZqASD1Q/6QbOXU2UfQsEeqyGCBH9Tap8vURNdhnhH4on JBSKWKByyi6nF2GZW2izrZMShBGR12EoKI0YVxztbok68uk5DyxpV013t/h1ceTSyYOe fBtExplfHhessvJX+QhDeb01f66O50AThzhrt0G4tgz5nbo1dZJAIaKJIcg9brjlDwP2 UmQuy9xrh6EBP5XXdNuGDvuIUQzK98YkL3x+F4imxJYoboOSIylUtF9MT5QKvNjdTpF0 YWkg== X-Gm-Message-State: AOAM532cySDIEZ67ymBJoZkLsy6GnO876ZE+ftOtzOU4NaaLI3Qrc1y2 QMeryJBreO9flAgCyfN922kiXkHiMOpiNYsa X-Google-Smtp-Source: ABdhPJwkuPAMRxe2gn3Rp4yNcFks11UfpKSvT2HeY3VS+w0eKLCk6XyxGNIT590asHY71Swa8UIh7g== X-Received: by 2002:a2e:505:: with SMTP id 5mr33522054ljf.310.1635800490330; Mon, 01 Nov 2021 14:01:30 -0700 (PDT) Received: from mail-lf1-f50.google.com (mail-lf1-f50.google.com. [209.85.167.50]) by smtp.gmail.com with ESMTPSA id x20sm1500854lfu.196.2021.11.01.14.01.29 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 01 Nov 2021 14:01:29 -0700 (PDT) Received: by mail-lf1-f50.google.com with SMTP id c28so38677491lfv.13 for ; Mon, 01 Nov 2021 14:01:29 -0700 (PDT) X-Received: by 2002:a05:6512:10c3:: with SMTP id k3mr30843900lfg.150.1635800489198; Mon, 01 Nov 2021 14:01:29 -0700 (PDT) MIME-Version: 1.0 References: <163572864256.3357115.931779940195622047.tglx@xen13> <163572864855.3357115.17938524897008353101.tglx@xen13> In-Reply-To: <163572864855.3357115.17938524897008353101.tglx@xen13> From: Linus Torvalds Date: Mon, 1 Nov 2021 14:01:13 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT pull] sched/core for v5.16-rc1 To: Thomas Gleixner Cc: Linux Kernel Mailing List , "the arch/x86 maintainers" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Oct 31, 2021 at 6:16 PM Thomas Gleixner wrote: > > - Make wchan() more robust and work with all kind of unwinders by > enforcing that the task stays blocked while unwinding is in progress. Ugh. This not-very-important data is protected by a rather core lock. Is this yet another example of "unwinding is so fragile that it can screw up unless we take a lock that is seriously overkill for a not very important operation"? Unwinders that need locks because they can do bad things if they are working on unstable data are EVIL and WRONG. I guess I don't care too much about the pi_lock, and the actual unwinding is hopefully done on tasks that don't care about it, but this smells suspicious to me. Why is that "stable wchan" so magically important? Linus