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 D08F7C43219 for ; Mon, 9 May 2022 05:47:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235107AbiEIFtG (ORCPT ); Mon, 9 May 2022 01:49:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48922 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235007AbiEIFq3 (ORCPT ); Mon, 9 May 2022 01:46:29 -0400 Received: from mail-wm1-f49.google.com (mail-wm1-f49.google.com [209.85.128.49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B8F7A15E498; Sun, 8 May 2022 22:42:36 -0700 (PDT) Received: by mail-wm1-f49.google.com with SMTP id 125-20020a1c1983000000b003941f354c62so7614128wmz.0; Sun, 08 May 2022 22:42:36 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=PgUJQCGuVuN7RMUt/u/GB2vkYIZJaEjDbMnifyGw+XM=; b=uWYHN/OTPaoS3Qf10LSpocUCCLihQH0lh6ZiwjMj9Rtsb3OJYGFaBLfkbhP2sRjEEo +MQtww0LFDu9g394XKJlkHNE9/F3jnwxdbpWjb0Tp/HRV75iiQzEMiXWRfeZt5xnH0R1 7PfJmAJrL7NxAP3Ack+LcTXerTbXkUKnIXIuLOq4U9WBzXUIqoaSKHgfSYNCOfp9aWOl LMRF1A9EQWp3P/YotgFrhDZMAEf8w4NtIq3E5FdHQDgJcYyxZI5H3la0gYa2pdFmumrR d2Tukv0VeIb5JILapRcrBya/+8ZhjsN5AR8MqMWmaqbJZKjxUdIxO/uqKnnbDVDlhjAy JgZA== X-Gm-Message-State: AOAM530hKvIzA/eORU6ymucSZcLJqZ6PB5mgmD8qAeZSP2GWo4WnM1Ia uuAqbTGB3HU1geQ2IkqPWus= X-Google-Smtp-Source: ABdhPJwc4eYBOaGWeOZpzdHrP/EzHMr+8axHRm30/zjzwNtxs/nJxF3qH+zPotS6vDu9D2X/XzPbUQ== X-Received: by 2002:a05:600c:3b11:b0:394:57eb:c58b with SMTP id m17-20020a05600c3b1100b0039457ebc58bmr20723567wms.3.1652074950839; Sun, 08 May 2022 22:42:30 -0700 (PDT) Received: from ?IPV6:2a0b:e7c0:0:107::70f? ([2a0b:e7c0:0:107::70f]) by smtp.gmail.com with ESMTPSA id d7-20020adffbc7000000b0020c66310845sm9972919wrs.55.2022.05.08.22.42.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 08 May 2022 22:42:30 -0700 (PDT) Message-ID: Date: Mon, 9 May 2022 07:42:12 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH v1] serial: meson: acquire port->lock in startup() Content-Language: en-US To: John Ogness , Greg Kroah-Hartman , Neil Armstrong , Kevin Hilman Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, Jerome Brunet , Martin Blumenstingl , linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-amlogic@lists.infradead.org, Marek Szyprowski References: <20220508103547.626355-1-john.ogness@linutronix.de> From: Jiri Slaby In-Reply-To: <20220508103547.626355-1-john.ogness@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08. 05. 22, 12:35, John Ogness wrote: > The uart_ops startup() callback is called without interrupts > disabled and without port->lock locked, relatively late during the > boot process (from the call path of console_on_rootfs()). If the > device is a console, it was already previously registered and could > be actively printing messages. > > Since the startup() callback is reading/writing registers used by > the console write() callback (AML_UART_CONTROL), its access must > be synchronized using the port->lock. Currently it is not. > > The startup() callback is the only function that explicitly enables > interrupts. Without the synchronization, it is possible that > interrupts become accidentally permanently disabled. > > CPU0 CPU1 > meson_serial_console_write meson_uart_startup > -------------------------- ------------------ > spin_lock(port->lock) > val = readl(AML_UART_CONTROL) > uart_console_write() > writel(INT_EN, AML_UART_CONTROL) > writel(val, AML_UART_CONTROL) > spin_unlock(port->lock) > > Add port->lock synchronization to meson_uart_startup() to avoid > racing with meson_serial_console_write(). > > Also add detailed comments to meson_uart_reset() explaining why it > is *not* using port->lock synchronization. > > Link: https://lore.kernel.org/lkml/2a82eae7-a256-f70c-fd82-4e510750906e@samsung.com > Reported-by: Marek Szyprowski > Signed-off-by: John Ogness > Tested-by: Marek Szyprowski Makes sense to me. Reviewed-by: Jiri Slaby > --- > drivers/tty/serial/meson_uart.c | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c > index 2bf1c57e0981..39021dac09cc 100644 > --- a/drivers/tty/serial/meson_uart.c > +++ b/drivers/tty/serial/meson_uart.c > @@ -253,6 +253,14 @@ static const char *meson_uart_type(struct uart_port *port) > return (port->type == PORT_MESON) ? "meson_uart" : NULL; > } > > +/* > + * This function is called only from probe() using a temporary io mapping > + * in order to perform a reset before setting up the device. Since the > + * temporarily mapped region was successfully requested, there can be no > + * console on this port at this time. Hence it is not necessary for this > + * function to acquire the port->lock. (Since there is no console on this > + * port at this time, the port->lock is not initialized yet.) > + */ > static void meson_uart_reset(struct uart_port *port) > { > u32 val; > @@ -267,9 +275,12 @@ static void meson_uart_reset(struct uart_port *port) > > static int meson_uart_startup(struct uart_port *port) > { > + unsigned long flags; > u32 val; > int ret = 0; > > + spin_lock_irqsave(&port->lock, flags); > + > val = readl(port->membase + AML_UART_CONTROL); > val |= AML_UART_CLEAR_ERR; > writel(val, port->membase + AML_UART_CONTROL); > @@ -285,6 +296,8 @@ static int meson_uart_startup(struct uart_port *port) > val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2)); > writel(val, port->membase + AML_UART_MISC); > > + spin_unlock_irqrestore(&port->lock, flags); > + > ret = request_irq(port->irq, meson_uart_interrupt, 0, > port->name, port); > > > base-commit: 672c0c5173427e6b3e2a9bbb7be51ceeec78093a -- js suse labs