The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable@xxxxxxxxxxxxxxx>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 8679328eb859d06a1984ab48d90ac35d11bbcaf1 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable@xxxxxxxxxxxxxxx>' --in-reply-to '2023101533-spotty-alkalize-ac65@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 8679328eb859d06a1984ab48d90ac35d11bbcaf1 Mon Sep 17 00:00:00 2001 From: Lukas Wunner <lukas@xxxxxxxxx> Date: Thu, 21 Sep 2023 16:52:33 +0200 Subject: [PATCH] serial: Reduce spinlocked portion of uart_rs485_config() 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> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c index 7bdc21d5e13b..ca26a8aef2cb 100644 --- a/drivers/tty/serial/serial_core.c +++ b/drivers/tty/serial/serial_core.c @@ -1404,12 +1404,18 @@ static void uart_set_rs485_termination(struct uart_port *port, 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)); @@ -2474,11 +2480,10 @@ int uart_resume_port(struct uart_driver *drv, struct uart_port *uport) 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); @@ -2587,10 +2592,10 @@ uart_configure_port(struct uart_driver *drv, struct uart_state *state, 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.
