From: Sebastian Andrzej Siewior Date: Fri, 1 Mar 2024 22:45:31 +0100 Subject: [PATCH 18/18] serial: pch: Use uart_prepare_sysrq_char(). Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz The port lock is a spinlock_t which is becomes a sleeping lock on PREEMPT_RT. The driver splits the locking function into two parts: local_irq_save() and uart_port_lock() and this breaks PREEMPT_RT. Delay handling sysrq until port lock is dropped. Remove the special case in the console write routine an always use the complete locking function. Link: https://lore.kernel.org/r/20240301215246.891055-19-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior --- drivers/tty/serial/pch_uart.c | 24 +++++++++--------------- 1 file changed, 9 insertions(+), 15 deletions(-) --- a/drivers/tty/serial/pch_uart.c +++ b/drivers/tty/serial/pch_uart.c @@ -564,7 +564,7 @@ static int pch_uart_hal_read(struct eg20 if (uart_handle_break(port)) continue; } - if (uart_handle_sysrq_char(port, rbr)) + if (uart_prepare_sysrq_char(port, rbr)) continue; buf[i++] = rbr; @@ -1070,7 +1070,7 @@ static irqreturn_t pch_uart_interrupt(in handled |= (unsigned int)ret; } - uart_port_unlock(&priv->port); + uart_unlock_and_check_sysrq(&priv->port); return IRQ_RETVAL(handled); } @@ -1550,22 +1550,17 @@ pch_console_write(struct console *co, co { struct eg20t_port *priv; unsigned long flags; - int port_locked = 1; + int locked = 1; u8 ier; priv = pch_uart_ports[co->index]; touch_nmi_watchdog(); - local_irq_save(flags); - if (priv->port.sysrq) { - /* serial8250_handle_port() already took the port lock */ - port_locked = 0; - } else if (oops_in_progress) { - port_locked = uart_port_trylock(&priv->port); - } else { - uart_port_lock(&priv->port); - } + if (oops_in_progress) + locked = uart_port_trylock_irqsave(&priv->port, &flags); + else + uart_port_lock_irqsave(&priv->port, &flags); /* * First save the IER then disable the interrupts @@ -1583,9 +1578,8 @@ pch_console_write(struct console *co, co wait_for_xmitr(priv, UART_LSR_BOTH_EMPTY); iowrite8(ier, priv->membase + UART_IER); - if (port_locked) - uart_port_unlock(&priv->port); - local_irq_restore(flags); + if (locked) + uart_port_unlock_irqrestore(&priv->port, flags); } static int __init pch_console_setup(struct console *co, char *options)