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([2001:861:44c0:66c0:23c8:2656:fd52:f1cb]) by smtp.gmail.com with ESMTPSA id 11-20020a05600c264b00b0039444973258sm18402407wmy.0.2022.05.09.00.36.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 May 2022 00:36:38 -0700 (PDT) Message-ID: Date: Mon, 9 May 2022 09:36:40 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: [PATCH v1] serial: meson: acquire port->lock in startup() Content-Language: en-US To: John Ogness , Greg Kroah-Hartman , Kevin Hilman Cc: Petr Mladek , Sergey Senozhatsky , Steven Rostedt , linux-kernel@vger.kernel.org, Jiri Slaby , 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: Neil Armstrong Organization: Baylibre In-Reply-To: <20220508103547.626355-1-john.ogness@linutronix.de> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220509_003645_625553_6AF4CB3E X-CRM114-Status: GOOD ( 29.09 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 08/05/2022 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 > --- > 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 Thanks for fixing this, it may also fix an uart apparent lockup I encountered several time while developing on the platform, but the target was still alive so it matches. So I'll add: Fixes: ff7693d079e5 ("ARM: meson: serial: add MesonX SoC on-chip uart driver") and Acked-by: Neil Armstrong _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel