From: John Ogness <john.ogness@linutronix.de>
To: "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
Neil Armstrong <narmstrong@baylibre.com>,
Kevin Hilman <khilman@baylibre.com>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, Jiri Slaby <jirislaby@kernel.org>,
Jerome Brunet <jbrunet@baylibre.com>,
Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
linux-serial@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-amlogic@lists.infradead.org,
Marek Szyprowski <m.szyprowski@samsung.com>
Subject: [PATCH v1] serial: meson: acquire port->lock in startup()
Date: Sun, 8 May 2022 12:41:47 +0206 [thread overview]
Message-ID: <20220508103547.626355-1-john.ogness@linutronix.de> (raw)
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 <m.szyprowski@samsung.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
---
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
--
2.30.2
next reply other threads:[~2022-05-08 10:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-08 10:35 John Ogness [this message]
2022-05-09 5:42 ` [PATCH v1] serial: meson: acquire port->lock in startup() Jiri Slaby
2022-05-09 7:36 ` Neil Armstrong
2022-05-10 9:37 ` Petr Mladek
2022-05-10 9:49 ` Greg Kroah-Hartman
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