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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E139EC433EF for ; Tue, 24 May 2022 15:12:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237888AbiEXPMK (ORCPT ); Tue, 24 May 2022 11:12:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238872AbiEXPMD (ORCPT ); Tue, 24 May 2022 11:12:03 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 0B98F3D4BB for ; Tue, 24 May 2022 08:12:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1653405121; 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=ofqhF7B0Lhr9XDJpCI5NspBe7jXyy3A5iExBePEO86M=; b=hWN9iqCPVXBmCJ0YMMvLsB3VW+sjxTObcrcS642M4fkbZxk1Mhm7HkRuD13H5SUnLZ77EO qcIp5IRj0ktw9Jv7FvbtyjKClEt4JRcA4twu6KjY6aQ+UEpSnshUVAntCmJUzvsaB+K0Gm iTYop9+vHW+dz9Hh5BpIDEKeM6TEwww= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-368-ORQeLfTsMK6bE3vVpY43bw-1; Tue, 24 May 2022 11:11:54 -0400 X-MC-Unique: ORQeLfTsMK6bE3vVpY43bw-1 Received: by mail-wr1-f69.google.com with SMTP id e17-20020adfe391000000b0020e64e7dd15so4399432wrm.4 for ; Tue, 24 May 2022 08:11:54 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=ofqhF7B0Lhr9XDJpCI5NspBe7jXyy3A5iExBePEO86M=; b=RTMX77vBkxYYgKlsGyM8qeVkCpGdkHtFkjlMoTfePhPaZmFxlNUhxeL9p9zb81lGl+ tIvKkvWEwftZeYqunHJ8AMe2A0EdzcBx8fDAJSIUjEaJG+H40pTeb6XxMowbKTp+8DUB X4XAAWQNCF1b5jHmOvyNRnMnyy4RRexM8A3hh2BC2OkWg3okqPCaBaWAV1ehJYjtsHyy eOqsz0bEOYHyW78ZsnYdEowDgbxAz9++CgqAfG3XCkm0vOVZ2McCbX5yDNxaQtVXhsNg 8XBYV6Q5QSLrfig3XxzoiNKMrxzjJRQgw0O/vzEXndBv/YwMrbh1A8peLuecp4HG7FcO 59eQ== X-Gm-Message-State: AOAM530ShI+wZ9rka/df3f6ltZRbNR26aZ1q+Mo4k2yGQ22Z0OMthMM1 tlJnSqz59EIyig6EF9ZLvSqtamQMcA2ZM+i+tcnHkv+wnA82nzzRHjdqL+SVLNzG/YySz0E1X00 Bdwlp6REB0Rn7rhXb/5Vwg2x+ X-Received: by 2002:a05:600c:354a:b0:394:8fa4:73bc with SMTP id i10-20020a05600c354a00b003948fa473bcmr4204448wmq.37.1653405112862; Tue, 24 May 2022 08:11:52 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzN72fmnvYSWbgO8JmvvLE5huJ+2BUFJSTipvlRfySv+pMVULvp/Gj0OiXV+/iI8xQuds0lrA== X-Received: by 2002:a05:600c:354a:b0:394:8fa4:73bc with SMTP id i10-20020a05600c354a00b003948fa473bcmr4204425wmq.37.1653405112626; Tue, 24 May 2022 08:11:52 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id m6-20020adfa3c6000000b0020fc4cd81f6sm10619841wrb.60.2022.05.24.08.11.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 May 2022 08:11:52 -0700 (PDT) From: Valentin Schneider To: Phil Auld , linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH] cpuhp: make target_store() a nop when target == state In-Reply-To: <20220523144728.32414-1-pauld@redhat.com> References: <20220523144728.32414-1-pauld@redhat.com> Date: Tue, 24 May 2022 16:11:51 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/05/22 10:47, Phil Auld wrote: > writing the current state back into hotplug/target calls cpu_down() > which will set cpu dying even when it isn't and then nothing will > ever clear it. A stress test that reads values and writes them back > for all cpu device files in sysfs will trigger the BUG() in > select_fallback_rq once all cpus are marked as dying. > > kernel/cpu.c::target_store() > ... > if (st->state < target) > ret = cpu_up(dev->id, target); > else > ret = cpu_down(dev->id, target); > > cpu_down() -> cpu_set_state() > bool bringup = st->state < target; > ... > if (cpu_dying(cpu) != !bringup) > set_cpu_dying(cpu, !bringup); > > Make this safe by catching the case where target == state > and bailing early. > > Signed-off-by: Phil Auld > --- > > Yeah, I know... don't do that. But it's still messy. > > !< != > > > kernel/cpu.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index d0a9aa0b42e8..8a71b1149c60 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -2302,6 +2302,9 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr, > return -EINVAL; > #endif > > + if (target == st->state) > + return count; > + The current checks are against static boundaries, this has to compare against st->state - AFAICT this could race with another hotplug operation to the same CPU, e.g. CPU42.cpuhp_state ->state == CPUHP_AP_SCHED_STARTING ->target == CPUHP_ONLINE CPU42.cpuhp_state == CPUHP_ONLINE _cpu_up() has: /* * The caller of cpu_up() might have raced with another * caller. Nothing to do. */ if (st->state >= target) goto out; Looks like we want an equivalent in _cpu_down(), what do you think? > ret = lock_device_hotplug_sysfs(); > if (ret) > return ret; > -- > 2.18.0