Commit b06f3889 authored by Sean Anderson's avatar Sean Anderson Committed by Greg Kroah-Hartman
Browse files

tty: xilinx_uartps: split sysrq handling 



lockdep detects the following circular locking dependency:

CPU 0                      CPU 1
========================== ============================
cdns_uart_isr()            printk()
  uart_port_lock(port)       console_lock()
			     cdns_uart_console_write()
                               if (!port->sysrq)
                                 uart_port_lock(port)
  uart_handle_break()
    port->sysrq = ...
  uart_handle_sysrq_char()
    printk()
      console_lock()

The fixed commit attempts to avoid this situation by only taking the
port lock in cdns_uart_console_write if port->sysrq unset. However, if
(as shown above) cdns_uart_console_write runs before port->sysrq is set,
then it will try to take the port lock anyway. This may result in a
deadlock.

Fix this by splitting sysrq handling into two parts. We use the prepare
helper under the port lock and defer handling until we release the lock.

Fixes: 74ea66d4 ("tty: xuartps: Improve sysrq handling")
Signed-off-by: default avatarSean Anderson <sean.anderson@linux.dev>
Cc: stable@vger.kernel.org # c9802481: serial: xilinx_uartps: Use port lock wrappers
Acked-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Link: https://lore.kernel.org/r/20250110213822.2107462-1-sean.anderson@linux.dev


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 568bfce0

drivers/tty/serial/xilinx_uartps.c

+3 −5
Original line number Diff line number Diff line
@@ -287,7 +287,7 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus) 
				continue;

		}



		if (uart_handle_sysrq_char(port, data))

		if (uart_prepare_sysrq_char(port, data))

			continue;



		if (is_rxbs_support) {
@@ -495,7 +495,7 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id) 
	    !(readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS))

		cdns_uart_handle_rx(dev_id, isrstatus);



	uart_port_unlock(port);

	uart_unlock_and_check_sysrq(port);

	return IRQ_HANDLED;

}
@@ -1380,9 +1380,7 @@ static void cdns_uart_console_write(struct console *co, const char *s, 
	unsigned int imr, ctrl;

	int locked = 1;



	if (port->sysrq)

		locked = 0;

	else if (oops_in_progress)

	if (oops_in_progress)

		locked = uart_port_trylock_irqsave(port, &flags);

	else

		uart_port_lock_irqsave(port, &flags);