Re: UART/TTY console deadlock

[S, Shirish]

On 6/30/2020 11:32 PM, Tony Lindgren wrote:
> * Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx> [200630 13:06]:
> > On (20/06/30 14:22), Petr Mladek wrote:
> ...
>
> > > > > > @@ -2284,8 +2289,6 @@ 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);
> > > > > >   
> > > > > >   		wait_for_xmitr(up, UART_LSR_THRE);
> > > > > >   		serial_port_out_sync(port, UART_IER, UART_IER_THRI);
> > > > > > @@ -2297,9 +2300,9 @@ 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);
> > > > > >   		spin_unlock_irqrestore(&port->lock, flags);
> > > > > > +		if (irq_shared)
> > > > > > +			enable_irq(port->irq);
> > > > > >   
> > > > > >   		/*
> > > > > >   		 * If the interrupt is not reasserted, or we otherwise
> > > > > I think that it might be safe but I am not 100% sure, sigh.
> > > > Yeah, I'm not 100%, but I'd give it a try.
> > > I do not feel brave enough to ack it today. But I am all for trying it
> > > if anyone more familiar with the code is fine with it.
> > I see. Well, I suppose we need Ack-s from tty/serial/8250 maintainers.
> > I would not be very happy if _only_ printk people Ack the patch.

FWIW, the lockdep trace is not seen anymore with the patch applied.

Regards,

Shirish S

> 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().
>
> The other device for irq_shared should be capable of dealing
> with spurious interrupts if it's shared.
>
> Regards,
>
> Tony

--
Regards,
Shirish S