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=-2.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 2CA4DC04A6B for ; Fri, 10 May 2019 05:51:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F032020656 for ; Fri, 10 May 2019 05:50:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="pUfvvAZF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727057AbfEJFu6 (ORCPT ); Fri, 10 May 2019 01:50:58 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:46579 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726924AbfEJFu6 (ORCPT ); Fri, 10 May 2019 01:50:58 -0400 Received: by mail-pg1-f196.google.com with SMTP id t187so2430316pgb.13 for ; Thu, 09 May 2019 22:50:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=7DNbQy+XeUwJNnsLrbsf7GgVt3vG1E1+vrBOysMv8YE=; b=pUfvvAZFqUVTiqjxv40mkHsNUmq7PBox1pFF166ZopvOvdfQGvbOVJnOm+aoJu5sEz DOggZuoz45ZIDa8GI90MV1/vdHaAAtQI9uW956G/4MxykZgBJ2dWMiXvBvfSHjOFwgFO /H0TseWHxGUXAS4l8bz4i3L4KVPE7Ts5JNHc7z4SLbLGzOGL7XDZuY3s+d85vDTOMcBO 0KezU2gXMeA0eGAB4od6jTnHD0HZmFlH0OXeiTpfzy2NhQdcpFyHsUTxdOz8w2oL6U4o xXOdPK6D0yIW2TzK4KruW/bOPNR9VrQJG3ue4SDSTv3AHdmqAvYgCpT6pVAQyxERl4ge tf5A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=7DNbQy+XeUwJNnsLrbsf7GgVt3vG1E1+vrBOysMv8YE=; b=S4MN/yLrtReVtkbwURAwJxXU5FaCMd8LLsOcJp5DL8bFscBjY/ZMTefY9JtlyHiRkv UO/xgcVpeyfBIUJV1x0SuN0T+s8xsaBx3dMCCbYFbAqvVo4SceSQQgjwBPWRVW5VYdnB +rQdKt7Bb0LzZs96SDYq61O0SaaTurbxwKViWl8bdSVmQG9eYgc72LZuAJRi4ljOsZap b8xpAq9x1qa7mCpdGUuFLWs0h6dNhoh91FBpr4uY0Ihonqwv7KCfOLPqj7BwlnUWwGdE m/HuaZoDRqnpM3W0Eho94ObYf9Lq59ZYgSZwNUQnmWdX1LkETDFqeImd/fd89iiokQfm 9m2w== X-Gm-Message-State: APjAAAXlOyzZxxZmubrEdTV/kV7rv9TNkuGrE1cW+nYeWUm71EK3o3to RShIININiHjZOdM5V/8Owko= X-Google-Smtp-Source: APXvYqzoTTJJuY7emFpyseXgmhhtAkOmA0sg3IQDQa3Kp5WUeM/5FO2g9Cz09UPUzVof3g3O+Df1Sg== X-Received: by 2002:a63:a55:: with SMTP id z21mr11336025pgk.440.1557467457679; Thu, 09 May 2019 22:50:57 -0700 (PDT) Received: from localhost ([39.7.15.25]) by smtp.gmail.com with ESMTPSA id i12sm4613535pgb.61.2019.05.09.22.50.55 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 09 May 2019 22:50:56 -0700 (PDT) Date: Fri, 10 May 2019 14:50:53 +0900 From: Sergey Senozhatsky To: Daniel Vetter Cc: Intel Graphics Development , DRI Development , Daniel Vetter , Peter Zijlstra , Ingo Molnar , Will Deacon , Petr Mladek , Sergey Senozhatsky , Steven Rostedt , John Ogness , Chris Wilson , linux-kernel@vger.kernel.org Subject: Re: [PATCH] kernel/locking/semaphore: use wake_q in up() Message-ID: <20190510055053.GA9864@jagdpanzerIV> References: <20190509120903.28939-1-daniel.vetter@ffwll.ch> <20190509200633.19678-1-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190509200633.19678-1-daniel.vetter@ffwll.ch> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (05/09/19 22:06), Daniel Vetter wrote: [..] > +/* Functions for the contended case */ > + > +struct semaphore_waiter { > + struct list_head list; > + struct task_struct *task; > + bool up; > +}; > + > /** > * up - release the semaphore > * @sem: the semaphore to release > @@ -179,24 +187,25 @@ EXPORT_SYMBOL(down_timeout); > void up(struct semaphore *sem) > { > unsigned long flags; > + struct semaphore_waiter *waiter; > + DEFINE_WAKE_Q(wake_q); > > raw_spin_lock_irqsave(&sem->lock, flags); > - if (likely(list_empty(&sem->wait_list))) > + if (likely(list_empty(&sem->wait_list))) { > sem->count++; > - else > - __up(sem); > + } else { > + waiter = list_first_entry(&sem->wait_list, > + struct semaphore_waiter, list); > + list_del(&waiter->list); > + waiter->up = true; > + wake_q_add(&wake_q, waiter->task); > + } > raw_spin_unlock_irqrestore(&sem->lock, flags); So the new code still can printk/WARN under sem->lock in some buggy cases. E.g. wake_q_add() get_task_struct() refcount_inc_checked() WARN_ONCE() Are we fine with that? -ss