Re: [PATCH v3] serial: imx: Suppress false positive sysrq lockdep warning

[Fabio Estevam <festevam@denx.de>]

On 01/10/2021 10:56, Johan Hovold wrote:

> No, no, no.
> 
> Just replace this unlock with uart_unlock_and_check_sysrq() and do the
> corresponding change in imx_uart_int(). The result is an even smaller
> diff than what you're currently proposing and without any performance
> penalty from dropping and reacquiring the lock.

Just to be clear, this is something that I have also tried:

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 8b121cd869e9..b652908f0bf1 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -803,7 +803,7 @@ static irqreturn_t __imx_uart_rxint(int irq, void 
*dev_id)
  				continue;
  		}

-		if (uart_handle_sysrq_char(&sport->port, (unsigned char)rx))
+		if (uart_prepare_sysrq_char(&sport->port, (unsigned char)rx))
  			continue;

  		if (unlikely(rx & URXD_ERR)) {
@@ -858,7 +858,7 @@ static irqreturn_t imx_uart_rxint(int irq, void 
*dev_id)

  	ret = __imx_uart_rxint(irq, dev_id);

-	spin_unlock(&sport->port.lock);
+	uart_unlock_and_check_sysrq(&sport->port);

  	return ret;
  }
@@ -991,7 +991,7 @@ static irqreturn_t imx_uart_int(int irq, void 
*dev_id)
  		ret = IRQ_HANDLED;
  	}

-	spin_unlock(&sport->port.lock);
+	uart_unlock_and_check_sysrq(&sport->port);

  	return ret;
  }
@@ -1977,9 +1977,7 @@ imx_uart_console_write(struct console *co, const 
char *s, unsigned int count)
  	unsigned int ucr1;
  	int locked = 1;

-	if (sport->port.sysrq)
-		locked = 0;
-	else if (oops_in_progress)
+	if (oops_in_progress)
  		locked = spin_trylock_irqsave(&sport->port.lock, flags);
  	else
  		spin_lock_irqsave(&sport->port.lock, flags);

, but still get the lockdep warning in this case.

Thanks