From 4e508c59357310a41b8fa69a576dfea4208f2518 Mon Sep 17 00:00:00 2001 From: Phil Elwell Date: Wed, 16 Feb 2022 16:08:02 +0000 Subject: [PATCH] sc16is7xx: Fix for incorrect data being transmitted commit eebb0f4e894f1e9577a56b337693d1051dd6ebfd upstream. UART drivers are meant to use the port spinlock within certain methods, to protect against reentrancy. The sc16is7xx driver does very little locking, presumably because when added it triggers "scheduling while atomic" errors. This is due to the use of mutexes within the regmap abstraction layer, and the mutex implementation's habit of sleeping the current thread while waiting for access. Unfortunately this lack of interlocking can lead to corruption of outbound data, which occurs when the buffer used for I2C transmission is used simultaneously by two threads - a work queue thread running sc16is7xx_tx_proc, and an IRQ thread in sc16is7xx_port_irq, both of which can call sc16is7xx_handle_tx. An earlier patch added efr_lock, a mutex that controls access to the EFR register. This mutex is already claimed in the IRQ handler, and all that is required is to claim the same mutex in sc16is7xx_tx_proc. See: https://github.com/raspberrypi/linux/issues/4885 Fixes: 6393ff1c4435 ("sc16is7xx: Use threaded IRQ") Cc: stable Signed-off-by: Phil Elwell Link: https://lore.kernel.org/r/20220216160802.1026013-1-phil@raspberrypi.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/sc16is7xx.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index acbb615dd28fd..0ab788058fa2a 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -734,12 +734,15 @@ static irqreturn_t sc16is7xx_irq(int irq, void *dev_id) static void sc16is7xx_tx_proc(struct kthread_work *ws) { struct uart_port *port = &(to_sc16is7xx_one(ws, tx_work)->port); + struct sc16is7xx_port *s = dev_get_drvdata(port->dev); if ((port->rs485.flags & SER_RS485_ENABLED) && (port->rs485.delay_rts_before_send > 0)) msleep(port->rs485.delay_rts_before_send); + mutex_lock(&s->efr_lock); sc16is7xx_handle_tx(port); + mutex_unlock(&s->efr_lock); } static void sc16is7xx_reconf_rs485(struct uart_port *port)