linux-kernel - Re: UART/TTY console deadlock

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Date:   Wed, 1 Jul 2020 12:14:35 +0530
From:   "S, Shirish" <sshankar@....com>
To:     Tony Lindgren <tony@...mide.com>,
        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


On 6/30/2020 11:32 PM, Tony Lindgren wrote:
> * Sergey Senozhatsky <sergey.senozhatsky@...il.com> [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