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 D2641C433EF for ; Fri, 27 May 2022 09:38:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350626AbiE0Jil (ORCPT ); Fri, 27 May 2022 05:38:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350599AbiE0Jid (ORCPT ); Fri, 27 May 2022 05:38:33 -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 3FBBA4BFC2 for ; Fri, 27 May 2022 02:38:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1653644309; 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=jWBfsIbPUgPp+IdgwSvqqfPkbnVArM00S/JeXJWx878=; b=LuvCXkhgvSY7SimrhUg58SDKzMZz+5qKUZgrX/cBYO8KZjUnkyKUpZh9pbq8w2Nqa4ByIg J5deOFId5F/IReV/d6sEOmR3NPeAfwkYrZ1xfpZQnWlt/Fds+7f5jXbCMmgSjrxvkGOoA1 mkDIRwPiMQDTPGzEyNRPXfgxBf2Q42E= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-530-bU2VpNFFNLul-I8BdqfU-A-1; Fri, 27 May 2022 05:38:28 -0400 X-MC-Unique: bU2VpNFFNLul-I8BdqfU-A-1 Received: by mail-wr1-f72.google.com with SMTP id w17-20020adf8bd1000000b0020fc99aee61so695890wra.18 for ; Fri, 27 May 2022 02:38:28 -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=jWBfsIbPUgPp+IdgwSvqqfPkbnVArM00S/JeXJWx878=; b=ERaZBc2VrJ2EJvS1sdcXioE5NVMo5buuVzCc8vTXSn+tWnkquICZD45hLkbd0t0kiK 9adTFJTto4ySrcLgPh1hmRVNI91lmSFHDiKY+SsmXLZJdv2bfC71A/qUnfDDmQ8Hb6nk +SexoDaXbmrcfV6skYp0RNBlwIcS4S2PeOk+gHlubySoeTs8F687cDX6wnZxUF4ZqZs8 oIKf6qO+IhTHfW96OVFDWPK7DLu/JLhcLrcqcR5/ipsydkfIY7rs/B6mSFwck2rW1fk2 ed55GBrvz9EuzrdBldzEEwuYUD5X66oK3IQV+A1FA/GukKUJ1kwpQY9NsUAV66L3X5Fh vUOw== X-Gm-Message-State: AOAM533EHGgF0UDhPCwJIk3abSyJcBcPdgKK+YlaRUM6xLWBgeyC90g2 vlsFwmECg0J1rtor4c7TF9ArQrgfBjssaueIrbSGIkHiNkN+MgT1gbfYSOXAvTFMXWIvL2UDgik dZCXZQ5gn4hm9Z3K6a2qteaaB X-Received: by 2002:a5d:525b:0:b0:20c:e010:b9f3 with SMTP id k27-20020a5d525b000000b0020ce010b9f3mr33297156wrc.291.1653644306389; Fri, 27 May 2022 02:38:26 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw9dc/h6KnzcMF+c7w6r1D7Te0EsYMnDtoc3WdL3pOVVx8wuoMD5Yc1AuMYCRF28+tQg0N+pg== X-Received: by 2002:a5d:525b:0:b0:20c:e010:b9f3 with SMTP id k27-20020a5d525b000000b0020ce010b9f3mr33297141wrc.291.1653644306042; Fri, 27 May 2022 02:38:26 -0700 (PDT) Received: from vschneid.remote.csb ([185.11.37.247]) by smtp.gmail.com with ESMTPSA id j17-20020a05600c191100b00397393419e3sm1815525wmq.28.2022.05.27.02.38.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 May 2022 02:38:25 -0700 (PDT) From: Valentin Schneider To: Phil Auld , linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH v2 1/2] cpuhp: make target_store() a nop when target == state In-Reply-To: <20220526160615.7976-2-pauld@redhat.com> References: <20220526160615.7976-1-pauld@redhat.com> <20220526160615.7976-2-pauld@redhat.com> Date: Fri, 27 May 2022 10:38:24 +0100 Message-ID: MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 26/05/22 12:06, Phil Auld wrote: > writing the current state back in 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); > > Fix this by letting state==target fall through in the target_store() > conditional. > To go back on my data race paranoia: writes to both cpu$x/online and cpu$x/hotplug/target are serialized by device_hotplug_lock, and so are the exported kernel hotplug functions ({add, remove}_cpu()). That's not cpu_add_remove_lock as I was looking for, but that's still all under one lock, so I think we're good. Sorry for that! > Signed-off-by: Phil Auld Reviewed-by: Valentin Schneider > --- > kernel/cpu.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/cpu.c b/kernel/cpu.c > index d0a9aa0b42e8..cdb6ac10ad94 100644 > --- a/kernel/cpu.c > +++ b/kernel/cpu.c > @@ -2315,7 +2315,7 @@ static ssize_t target_store(struct device *dev, struct device_attribute *attr, > > if (st->state < target) > ret = cpu_up(dev->id, target); > - else > + else if (st->state > target) > ret = cpu_down(dev->id, target); > out: > unlock_device_hotplug(); > -- > 2.18.0