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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 0A41FC432C0 for ; Thu, 21 Nov 2019 18:33:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D2EAF2067D for ; Thu, 21 Nov 2019 18:33:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574361182; bh=wE2tHf3ZYWYbliD+R/Z0yBNHf5NZkidjFVls8TJM8C0=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=uREcq0ealAL/AVvGysn8y4QeAxgLJA7KladlSsv53nZqjjsQhv/pTQcyLOybxkZBG 5X/d135h3aY/235j32ppDneNjjMyo6IjnWa9RJYTYh3aSTqduCNOrvWaPCOfAP1lBr 5UCoWVRSW3lDHbVG1N+wLgTZgL1JkYlnZdYvBk+k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726968AbfKUSdB (ORCPT ); Thu, 21 Nov 2019 13:33:01 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:52173 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726293AbfKUSdB (ORCPT ); Thu, 21 Nov 2019 13:33:01 -0500 Received: by mail-wm1-f68.google.com with SMTP id g206so4603074wme.1 for ; Thu, 21 Nov 2019 10:33:00 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=QpdFGCi5ivXxDIzboDWyNYO66cHHS/lXg7ziVev9IZo=; b=jgCStv+qGqRqOTsBMWfs2Jen+gMWWaUoAyhn0xoaM56h0671j8K3ZpBnXIqKTolMly PunnmPMGBqBe2PWVlSJ3OxfES+8WRolNvYNd4C7jJb8ctYk33ZZj1jA2FI4ujcthwzLa oi6vKi84bgrulrqNHINLZKKcPRK7EHcIbNITnG8Nzl5Dc2txlK4RtHY/vwBdCJbJxics LNP2F9LhLW+/juuQ4N+/eIfgwd0IOfvCRs6+JTnUOiKphpVQECIdIARC3gE7JDMG/fCg 3yx8FBYoMWJhUwBge7uNaKxEg6e5QoGb1ybUb5y+16ppzoSlyDQv6sdVhxPq5U3cWJ6b iE1g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to:user-agent; bh=QpdFGCi5ivXxDIzboDWyNYO66cHHS/lXg7ziVev9IZo=; b=oUgda+sqBU0LI1Finmci9d4W8UXF2Wy+F0/lJgVEHvh/GmtOKdUMozYvwaCAA7wGQV T4cZF699TpAFCrN2AaFVUIFeSEBIxDmDVC4Bsne4zBhPCH+5z7BlT/wY4wjnIwlsmf2z G+5h9t1YhWfioNEMxkmBaDepn3pyepGXqoU5ZA4htO2SwQJBXlj8iI9gvW/fGh43/92J GiSWsM3PauSm8I3PYxdh9IyILKSO1bKFyAzow6CB8FH7qQSbU6t8DPuKhbufXBBQRJtm xr4o0jyEytZuxzQQL8ihdXe38hs9vStNwoqmnRw+rqU6e92zFXJfNsiMFwEhuJk2V/fK w9Gg== X-Gm-Message-State: APjAAAXM+rVxBDBzL/gAUsuJLG5ROQ0Ue5KwIyZ1RFxnd6Vaza5Cko1V YYQHI+joneNFck2qCmOMg8Q= X-Google-Smtp-Source: APXvYqxGdwJCh/RRx1XOPoqG1UX9YkIrYDWrkN5YLSJmIqCy3k62JPFmw42dzBYNc2cawVlYml+ZJQ== X-Received: by 2002:a7b:cc13:: with SMTP id f19mr12081590wmh.81.1574361179554; Thu, 21 Nov 2019 10:32:59 -0800 (PST) Received: from gmail.com (54033286.catv.pool.telekom.hu. [84.3.50.134]) by smtp.gmail.com with ESMTPSA id t185sm526758wmf.45.2019.11.21.10.32.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Nov 2019 10:32:59 -0800 (PST) Date: Thu, 21 Nov 2019 19:32:57 +0100 From: Ingo Molnar To: Marco Elver Cc: peterz@infradead.org, mingo@redhat.com, will@kernel.org, linux-kernel@vger.kernel.org, Qian Cai , Thomas Gleixner Subject: Re: [PATCH] spinlock_debug: Fix various data races Message-ID: <20191121183257.GA124760@gmail.com> References: <20191120155715.28089-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191120155715.28089-1-elver@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Marco Elver wrote: > static inline void debug_spin_lock_after(raw_spinlock_t *lock) > { > - lock->owner_cpu = raw_smp_processor_id(); > - lock->owner = current; > + WRITE_ONCE(lock->owner_cpu, raw_smp_processor_id()); > + WRITE_ONCE(lock->owner, current); > } debug_spin_lock_after() runs inside the spinlock itself - why do these writes have to be WRITE_ONCE()? > @@ -197,8 +197,8 @@ static inline void debug_write_unlock(rwlock_t *lock) > RWLOCK_BUG_ON(lock->owner != current, lock, "wrong owner"); > RWLOCK_BUG_ON(lock->owner_cpu != raw_smp_processor_id(), > lock, "wrong CPU"); > - lock->owner = SPINLOCK_OWNER_INIT; > - lock->owner_cpu = -1; > + WRITE_ONCE(lock->owner, SPINLOCK_OWNER_INIT); > + WRITE_ONCE(lock->owner_cpu, -1); > } This too is running inside the critical section of the spinlock - why are the WRITE_ONCE() calls necessary? Thanks, Ingo