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 565A9C3DA7D for ; Tue, 3 Jan 2023 09:00:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236898AbjACJAC (ORCPT ); Tue, 3 Jan 2023 04:00:02 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237108AbjACI75 (ORCPT ); Tue, 3 Jan 2023 03:59:57 -0500 Received: from mail-ej1-f41.google.com (mail-ej1-f41.google.com [209.85.218.41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1921DFED; Tue, 3 Jan 2023 00:59:56 -0800 (PST) Received: by mail-ej1-f41.google.com with SMTP id tz12so72046747ejc.9; Tue, 03 Jan 2023 00:59:56 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:in-reply-to:from:references:cc:to :content-language:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=MCnHYwwZj7hf09BfA6BHyTHlj6ziwHCFkuL5r8JlPOA=; b=3UB2TlncEmGraNcuKFdFWVv6G0QXuXahuYpW8XfbVAf/auOcxG/Dpg0zVAGtvTBjEd QXMYECYpMtR91Zuad+Yc7u2avDwANa6CDRfzGoj3G1APjwUBlPdWDLRcLpAh4MSO51Iv 1k3oMN0JCY0+wLW94bATR6c0ohdvW8bl+5sD8YiCQs4dtKbZ+NSq0E1JBfVkg4NOt9tk B9LkOQo/WGp3tv9aSh5SAZaEdMxSVcdH0xNsFM+YCOI50urzHaPqkOc/QSpjvVI76FV+ lLxb5JnJmtT5PoEcQL0LQcKtPRYdGHyN3yj8Y1lUPoYkE06CKBTJ/Gx+JZWA2hSwmgEE HRXQ== X-Gm-Message-State: AFqh2kqbLfSohb3trKddlzM3OMTG5PnMq/EkhAd4uYxdsDywSWQxNIQb joJmeEdmggDqfK/gX8tq2lXsyW9aWFo= X-Google-Smtp-Source: AMrXdXvcP1oGDt/E0YoVGqFqd8qZMTeJ6LyuXS9DMAb0Wb1kAju/36tyX6fdevafL0MBe6S1FJb+FA== X-Received: by 2002:a17:906:4e4b:b0:7c1:4040:ef17 with SMTP id g11-20020a1709064e4b00b007c14040ef17mr37017092ejw.54.1672736395375; Tue, 03 Jan 2023 00:59:55 -0800 (PST) Received: from ?IPV6:2a0b:e7c0:0:107::aaaa:49? ([2a0b:e7c0:0:107::aaaa:49]) by smtp.gmail.com with ESMTPSA id e23-20020a170906375700b007bfacaea851sm13838036ejc.88.2023.01.03.00.59.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Jan 2023 00:59:54 -0800 (PST) Message-ID: Date: Tue, 3 Jan 2023 09:59:52 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH v4 1/2] tty: serial: dz: convert atomic_* to refcount_* APIs for map_guard Content-Language: en-US To: Deepak R Varma , "Maciej W. Rozycki" , Greg Kroah-Hartman , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Saurabh Singh Sengar , Praveen Kumar References: From: Jiri Slaby In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On 26. 12. 22, 7:21, Deepak R Varma wrote: > The refcount_* APIs are designed to address known issues with the > atomic_t APIs for reference counting. They provide following distinct > advantages > - protect the reference counters from overflow/underflow > - avoid use-after-free errors > - provide improved memory ordering guarantee schemes > - neater and safer. Really? (see below) > --- a/drivers/tty/serial/dz.c > +++ b/drivers/tty/serial/dz.c ... > @@ -687,23 +686,19 @@ static int dz_map_port(struct uart_port *uport) > static int dz_request_port(struct uart_port *uport) > { > struct dz_mux *mux = to_dport(uport)->mux; > - int map_guard; > int ret; > > - map_guard = atomic_add_return(1, &mux->map_guard); > - if (map_guard == 1) { > - if (!request_mem_region(uport->mapbase, dec_kn_slot_size, > - "dz")) { > - atomic_add(-1, &mux->map_guard); > - printk(KERN_ERR > - "dz: Unable to reserve MMIO resource\n"); > + refcount_inc(&mux->map_guard); > + if (refcount_read(&mux->map_guard) == 1) { This is now racy, right? thanks, -- js suse labs