[bug report] serial: 8250: fix handle_irq locking

[bug report] serial: 8250: fix handle_irq locking

[Dan Carpenter]

Hello Johan Hovold,

The patch 853a9ae29e97: "serial: 8250: fix handle_irq locking" from
Jul 14, 2021, leads to the following Smatch static checker warning:

drivers/tty/serial/8250/8250_fsl.c:84 fsl8250_handle_irq() warn: inconsistent returns 'flags'.
  Locked on  : 38,46
  Unlocked on: 84

drivers/tty/serial/8250/8250_fsl.c
    26  int fsl8250_handle_irq(struct uart_port *port)
    27  {
    28          unsigned long flags;
    29          u16 lsr, orig_lsr;
    30          unsigned int iir;
    31          struct uart_8250_port *up = up_to_u8250p(port);
    32  
    33          spin_lock_irqsave(&up->port.lock, flags);
                                                  ^^^^^
    34  
    35          iir = port->serial_in(port, UART_IIR);
    36          if (iir & UART_IIR_NO_INT) {
    37                  spin_unlock(&up->port.lock);
    38                  return 0;

Needs to enable IRQs again.  Same below etc.

    39          }
    40  
    41          /* This is the WAR; if last event was BRK, then read and return */
    42          if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) {
    43                  up->lsr_saved_flags &= ~UART_LSR_BI;
    44                  port->serial_in(port, UART_RX);
    45                  spin_unlock(&up->port.lock);
    46                  return 1;
    47          }
    48  

regards,
dan carpenter

Re: [bug report] serial: 8250: fix handle_irq locking

[Johan Hovold]

On Mon, Feb 27, 2023 at 10:16:30AM +0300, Dan Carpenter wrote:
> Hello Johan Hovold,
> 
> The patch 853a9ae29e97: "serial: 8250: fix handle_irq locking" from
> Jul 14, 2021, leads to the following Smatch static checker warning:
> 
> drivers/tty/serial/8250/8250_fsl.c:84 fsl8250_handle_irq() warn: inconsistent returns 'flags'.
>   Locked on  : 38,46
>   Unlocked on: 84
> 
> drivers/tty/serial/8250/8250_fsl.c
>     26  int fsl8250_handle_irq(struct uart_port *port)
>     27  {
>     28          unsigned long flags;
>     29          u16 lsr, orig_lsr;
>     30          unsigned int iir;
>     31          struct uart_8250_port *up = up_to_u8250p(port);
>     32  
>     33          spin_lock_irqsave(&up->port.lock, flags);
>                                                   ^^^^^
>     34  
>     35          iir = port->serial_in(port, UART_IIR);
>     36          if (iir & UART_IIR_NO_INT) {
>     37                  spin_unlock(&up->port.lock);
>     38                  return 0;
> 
> Needs to enable IRQs again.  Same below etc.

Thanks, Dan. I just sent a fix here:

	https://lore.kernel.org/r/20230227085046.24282-1-johan@kernel.org

Johan