linux-kernel - Re: UART/TTY console deadlock

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Message-ID: <20200702160514.GK37466@atomide.com>
Date:   Thu, 2 Jul 2020 09:05:14 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Petr Mladek <pmladek@...e.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Raul Rangel <rrangel@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        kurt@...utronix.de, "S, Shirish" <Shirish.S@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        John Ogness <john.ogness@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: UART/TTY console deadlock

* Sergey Senozhatsky <sergey.senozhatsky@...il.com> [200702 05:13]:
> On (20/06/30 11:02), Tony Lindgren wrote:
> > This conditional disable for irq_shared does not look nice to me
> > from the other device point of view :)
> > 
> > Would it be possible to just set up te dummy interrupt handler
> > for the startup, then change it back afterwards? See for example
> > omap8250_no_handle_irq().
> 
> I think we can do it. serial8250_do_startup() and irq handler take
> port->lock, so they should be synchronized.
> 
> Something like this then?

Yeah thanks this should work better for shared irq.

Regards,

Tony

> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index f77bf820b7a3..61ad6f5f0f88 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2140,6 +2140,11 @@ static void serial8250_put_poll_char(struct uart_port *port,
>  
>  #endif /* CONFIG_CONSOLE_POLL */
>  
> +static int serial8250_dummy_handle_irq(struct uart_port *port)
> +{
> +	return 0;
> +}
> +
>  int serial8250_do_startup(struct uart_port *port)
>  {
>  	struct uart_8250_port *up = up_to_u8250p(port);
> @@ -2271,6 +2276,9 @@ int serial8250_do_startup(struct uart_port *port)
>  
>  	if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
>  		unsigned char iir1;
> +		int (*handler)(struct uart_port *);
> +
> +		handler = port->handle_irq;
>  		/*
>  		 * Test for UARTs that do not reassert THRE when the
>  		 * transmitter is idle and the interrupt has already
> @@ -2280,8 +2288,7 @@ int serial8250_do_startup(struct uart_port *port)
>  		 * allow register changes to become visible.
>  		 */
>  		spin_lock_irqsave(&port->lock, flags);
> -		if (up->port.irqflags & IRQF_SHARED)
> -			disable_irq_nosync(port->irq);
> +		port->handle_irq = serial8250_dummy_handle_irq;
>  
>  		wait_for_xmitr(up, UART_LSR_THRE);
>  		serial_port_out_sync(port, UART_IER, UART_IER_THRI);
> @@ -2293,8 +2300,7 @@ int serial8250_do_startup(struct uart_port *port)
>  		iir = serial_port_in(port, UART_IIR);
>  		serial_port_out(port, UART_IER, 0);
>  
> -		if (port->irqflags & IRQF_SHARED)
> -			enable_irq(port->irq);
> +		port->handle_irq = handler;
>  		spin_unlock_irqrestore(&port->lock, flags);
>  
>  		/*