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: 74ea66d4ca06 ("tty: xuartps: Improve sysrq handling")
Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # c980248179d: serial: xilinx_uartps: Use port lock wrappers
Acked-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250110213822.2107462-1-sean.anderson@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
[ resolved merge conflicts ]
Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxxx>
---
drivers/tty/serial/xilinx_uartps.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
index 2e5e86a00a77..7f83d2780017 100644
--- a/drivers/tty/serial/xilinx_uartps.c
+++ b/drivers/tty/serial/xilinx_uartps.c
@@ -268,7 +268,7 @@ 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) {
@@ -369,7 +369,7 @@ 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);
- spin_unlock(&port->lock);
+ uart_unlock_and_check_sysrq(port);
return IRQ_HANDLED;
}
@@ -1229,10 +1229,8 @@ 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)
- locked = spin_trylock_irqsave(&port->lock, flags);
+ if (oops_in_progress)
+ locked = uart_port_trylock_irqsave(port, &flags);
else
spin_lock_irqsave(&port->lock, flags);
--
2.35.1.1320.gc452695387.dirty
