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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 60579C433E0 for ; Mon, 18 May 2020 10:33:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 32CD020829 for ; Mon, 18 May 2020 10:33:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K6W8Z7f2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726739AbgERKdH (ORCPT ); Mon, 18 May 2020 06:33:07 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:32537 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726500AbgERKdG (ORCPT ); Mon, 18 May 2020 06:33:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589797984; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=fkZd+ATLBaLYev6yToKjV1ATICAP4OZcw+kqfR8rbuw=; b=K6W8Z7f28YGkHY36qZ2Pa/64PH+Bsg6dUmSPk0YExsAlBQZ1yOhu3Oqe8NNgvMRntZxILi NqX9CYQixFr7bDSgsfdBD5hdKkvzHfiMJ/2tkVR7lJf5Iype8Tie5AEzS376o3WinTsR6M QvO3oW84ULmc4j8G7LmwEF3Q2thanPU= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-257-qsx2yhhoNj-8xYwIYbgBFA-1; Mon, 18 May 2020 06:33:03 -0400 X-MC-Unique: qsx2yhhoNj-8xYwIYbgBFA-1 Received: by mail-wr1-f71.google.com with SMTP id e14so5452313wrv.11 for ; Mon, 18 May 2020 03:33:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=fkZd+ATLBaLYev6yToKjV1ATICAP4OZcw+kqfR8rbuw=; b=DOQTzeiGZNSaSwThn+WMKAVI4zjuCzVqbUf9J7vVHxkTV322aRtKTVerPwmFaot/N6 6IQ22/33TyFrtFwDJslYvxt1/jmjjeDjkmwFgXzWt/eYii5HQLw01rLT70k9jY5Kwy6B tzHwWqAAGj0aCReC1sClxhZlGEgNd4V1twQMrfmr15VTplTA4FC+fs9DDahvVl3zi1r5 0F3ESiXLFfpX5RwrN4VtCeoipZhWs1+nPJZFtHeo8yjidEYZWTjxp8k92j18DZZtqLJ5 Dqfyu306dvTvgLmAAEe7VxPfs0ATatr9rWGRJkhIh5XIiToCwDniDHga4aED6b3FpA+B XHvQ== X-Gm-Message-State: AOAM530xaYpwNixubdmjo0hb8eKwqYEvmG1JB9JV4i3N71EKUwmiLUQm o9+17lbUlGHW9HKyNP0srj08VY6/RwriosOBNowUZB4ocniH83KqQ0I3uoK9W3iF8VmbULSS0hw qH9wsYe3gRxPisdJGl6ezyxJU X-Received: by 2002:adf:e4c2:: with SMTP id v2mr18711373wrm.72.1589797981965; Mon, 18 May 2020 03:33:01 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzxaKQWu7YzReGiltWAyRl2hw4+e2C71C62VqLQpl2ItwOW1BspXytcsAQK4cMdA6ayUoHJxw== X-Received: by 2002:adf:e4c2:: with SMTP id v2mr18711347wrm.72.1589797981753; Mon, 18 May 2020 03:33:01 -0700 (PDT) Received: from [192.168.178.58] ([151.30.90.67]) by smtp.gmail.com with ESMTPSA id e21sm15457996wme.34.2020.05.18.03.33.00 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 18 May 2020 03:33:01 -0700 (PDT) Subject: Re: [PATCH 4/5] rcuwait: Introduce rcuwait_active() To: Davidlohr Bueso , tglx@linutronix.de Cc: peterz@infradead.org, maz@kernel.org, bigeasy@linutronix.de, rostedt@goodmis.org, torvalds@linux-foundation.org, will@kernel.org, joel@joelfernandes.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Davidlohr Bueso References: <20200424054837.5138-1-dave@stgolabs.net> <20200424054837.5138-5-dave@stgolabs.net> From: Paolo Bonzini Message-ID: <57309494-58bf-a11e-e4ac-e669e6af22f2@redhat.com> Date: Mon, 18 May 2020 12:33:00 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200424054837.5138-5-dave@stgolabs.net> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 24/04/20 07:48, Davidlohr Bueso wrote: > +/* > + * Note: this provides no serialization and, just as with waitqueues, > + * requires care to estimate as to whether or not the wait is active. > + */ > +static inline int rcuwait_active(struct rcuwait *w) > +{ > + return !!rcu_dereference(w->task); > +} This needs to be changed to rcu_access_pointer: --------------- 8< ----------------- From: Paolo Bonzini Subject: [PATCH] rcuwait: avoid lockdep splats from rcuwait_active() rcuwait_active only returns whether w->task is not NULL. This is exactly one of the usecases that are mentioned in the documentation for rcu_access_pointer() where it is correct to bypass lockdep checks. This avoids a splat from kvm_vcpu_on_spin(). Reported-by: Wanpeng Li Cc: Peter Zijlstra Signed-off-by: Paolo Bonzini diff --git a/include/linux/rcuwait.h b/include/linux/rcuwait.h index c1414ce44abc..61c56cca95c4 100644 --- a/include/linux/rcuwait.h +++ b/include/linux/rcuwait.h @@ -31,7 +31,7 @@ static inline void rcuwait_init(struct rcuwait *w) */ static inline int rcuwait_active(struct rcuwait *w) { - return !!rcu_dereference(w->task); + return !!rcu_access_pointer(w->task); } extern int rcuwait_wake_up(struct rcuwait *w); Paolo