From 71f42b2149a1307a97165b409493665579462ea0 Mon Sep 17 00:00:00 2001 From: Jacques Nilo Date: Wed, 13 May 2026 15:30:24 +0200 Subject: [PATCH] serial: 8250: dispatch SysRq character in serial8250_handle_irq() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit serial8250_handle_irq() captures a SysRq character into port->sysrq_ch inside serial8250_handle_irq_locked() via uart_prepare_sysrq_char() (reached from serial8250_read_char()). Dispatch of that captured character to handle_sysrq() is expected to happen at port-unlock time, through uart_unlock_and_check_sysrq[_irqrestore](). After commit 8324a54f604d ("serial: 8250: Add serial8250_handle_irq_locked()") the function was reduced to a wrapper that takes the port lock via guard(uart_port_lock_irqsave) whose destructor is plain uart_port_unlock_irqrestore(). The sysrq-aware unlock helper is no longer called, so port->sysrq_ch is captured but never dispatched: BREAK + SysRq key is consumed silently. This was the very condition Johan Hovold's 853a9ae29e978 ("serial: 8250: fix handle_irq locking", 2021) introduced uart_unlock_and_check_sysrq_irqrestore() to address. Switch to the new guard(uart_port_lock_check_sysrq_irqsave), whose destructor is the sysrq-aware unlock helper, restoring the pre-split behaviour. Update the Context: comment on serial8250_handle_irq_locked() so future HW-specific 8250 wrappers know to use the same guard or the explicit sysrq-aware unlock. Verified on RTL8196E with CONFIG_MAGIC_SYSRQ_SERIAL=y: BREAK + 'h' on the console UART produces the SysRq help dump in dmesg and the brk counter in /proc/tty/driver/serial increments correctly. Fixes: 8324a54f604d ("serial: 8250: Add serial8250_handle_irq_locked()") Cc: stable@vger.kernel.org Reviewed-by: Ilpo Järvinen Signed-off-by: Jacques Nilo Link: https://patch.msgid.link/52692ae6c3501f7940347cef364ad7fcacaab7e5.1778675349.git.jnilo@free.fr Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index af78cc02f38e..c66ba714caa5 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1784,7 +1784,10 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir) } /* - * Context: port's lock must be held by the caller. + * Context: port's lock must be held by the caller. The caller must + * release it via guard(uart_port_lock_check_sysrq_irqsave) or + * uart_unlock_and_check_sysrq_irqrestore(), which captures SysRq + * character on unlock. */ void serial8250_handle_irq_locked(struct uart_port *port, unsigned int iir) { @@ -1837,7 +1840,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) if (iir & UART_IIR_NO_INT) return 0; - guard(uart_port_lock_irqsave)(port); + guard(uart_port_lock_check_sysrq_irqsave)(port); serial8250_handle_irq_locked(port, iir); return 1;