This is a note to let you know that I've just added the patch titled
serial: Reduce spinlocked portion of uart_rs485_config()
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-reduce-spinlocked-portion-of-uart_rs485_config.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8679328eb859d06a1984ab48d90ac35d11bbcaf1 Mon Sep 17 00:00:00 2001
From: Lukas Wunner <lukas@xxxxxxxxx>
Date: Thu, 21 Sep 2023 16:52:33 +0200
Subject: serial: Reduce spinlocked portion of uart_rs485_config()
From: Lukas Wunner <lukas@xxxxxxxxx>
commit 8679328eb859d06a1984ab48d90ac35d11bbcaf1 upstream.
Commit 44b27aec9d96 ("serial: core, 8250: set RS485 termination GPIO in
serial core") enabled support for RS485 termination GPIOs behind i2c
expanders by setting the GPIO outside of the critical section protected
by the port spinlock. Access to the i2c expander may sleep, which
caused a splat with the port spinlock held.
Commit 7c7f9bc986e6 ("serial: Deassert Transmit Enable on probe in
driver-specific way") erroneously regressed that by spinlocking the
GPIO manipulation again.
Fix by moving uart_rs485_config() (the function manipulating the GPIO)
outside of the spinlocked section and acquiring the spinlock inside of
uart_rs485_config() for the invocation of ->rs485_config() only.
This gets us one step closer to pushing the spinlock down into the
->rs485_config() callbacks which actually need it. (Some callbacks
do not want to be spinlocked because they perform sleepable register
accesses, see e.g. sc16is7xx_config_rs485().)
Stack trace for posterity:
Voluntary context switch within RCU read-side critical section!
WARNING: CPU: 0 PID: 56 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch
Call trace:
rcu_note_context_switch
__schedule
schedule
schedule_timeout
wait_for_completion_timeout
bcm2835_i2c_xfer
__i2c_transfer
i2c_transfer
i2c_transfer_buffer_flags
regmap_i2c_write
_regmap_raw_write_impl
_regmap_bus_raw_write
_regmap_write
_regmap_update_bits
regmap_update_bits_base
pca953x_gpio_set_value
gpiod_set_raw_value_commit
gpiod_set_value_nocheck
gpiod_set_value_cansleep
uart_rs485_config
uart_add_one_port
pl011_register_port
pl011_probe
Fixes: 7c7f9bc986e6 ("serial: Deassert Transmit Enable on probe in driver-specific way")
Suggested-by: Lino Sanfilippo <LinoSanfilippo@xxxxxx>
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v6.1+
Link: https://lore.kernel.org/r/f3a35967c28b32f3c6432d0aa5936e6a9908282d.1695307688.git.lukas@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/serial_core.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1410,12 +1410,18 @@ static void uart_set_rs485_termination(s
static int uart_rs485_config(struct uart_port *port)
{
struct serial_rs485 *rs485 = &port->rs485;
+ unsigned long flags;
int ret;
+ if (!(rs485->flags & SER_RS485_ENABLED))
+ return 0;
+
uart_sanitize_serial_rs485(port, rs485);
uart_set_rs485_termination(port, rs485);
+ spin_lock_irqsave(&port->lock, flags);
ret = port->rs485_config(port, NULL, rs485);
+ spin_unlock_irqrestore(&port->lock, flags);
if (ret)
memset(rs485, 0, sizeof(*rs485));
@@ -2480,11 +2486,10 @@ int uart_resume_port(struct uart_driver
if (ret == 0) {
if (tty)
uart_change_line_settings(tty, state, NULL);
+ uart_rs485_config(uport);
spin_lock_irq(&uport->lock);
if (!(uport->rs485.flags & SER_RS485_ENABLED))
ops->set_mctrl(uport, uport->mctrl);
- else
- uart_rs485_config(uport);
ops->start_tx(uport);
spin_unlock_irq(&uport->lock);
tty_port_set_initialized(port, true);
@@ -2593,10 +2598,10 @@ uart_configure_port(struct uart_driver *
port->mctrl &= TIOCM_DTR;
if (!(port->rs485.flags & SER_RS485_ENABLED))
port->ops->set_mctrl(port, port->mctrl);
- else
- uart_rs485_config(port);
spin_unlock_irqrestore(&port->lock, flags);
+ uart_rs485_config(port);
+
/*
* If this driver supports console, and it hasn't been
* successfully registered yet, try to re-register it.
Patches currently in stable-queue which might be from lukas@xxxxxxxxx are
queue-6.5/xhci-preserve-rsvdp-bits-in-erstba-register-correctly.patch
queue-6.5/xhci-clear-ehb-bit-only-at-end-of-interrupt-handler.patch
queue-6.5/serial-reduce-spinlocked-portion-of-uart_rs485_config.patch
