From 4c96e6aeacf54d4c8c47beeb66c4a994cada0dc9 Mon Sep 17 00:00:00 2001 From: John Ogness Date: Sun, 8 May 2022 12:41:47 +0206 Subject: [PATCH] serial: meson: acquire port->lock in startup() [ Upstream commit 589f892ac8ef244e47c5a00ffd8605daa1eaef8e ] 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 Fixes: ff7693d079e5 ("ARM: meson: serial: add MesonX SoC on-chip uart driver") Reported-by: Marek Szyprowski Tested-by: Marek Szyprowski Reviewed-by: Petr Mladek Reviewed-by: Jiri Slaby Acked-by: Neil Armstrong Signed-off-by: John Ogness Link: https://lore.kernel.org/r/20220508103547.626355-1-john.ogness@linutronix.de Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- 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 efee393..62e6c1a 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); -- 2.7.4