Re: UART/TTY console deadlock

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>, Petr Mladek <pmladek@suse.com>,
	Raul Rangel <rrangel@google.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	kurt@linutronix.de, "S, Shirish" <Shirish.S@amd.com>,
	Peter Zijlstra <peterz@infradead.org>,
	John Ogness <john.ogness@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>
Subject: Re: UART/TTY console deadlock
Date: Sat, 4 Jul 2020 14:35:46 +0300	[thread overview]
Message-ID: <CAHp75VdvNi_LWv7QhEsm1vQikeiMpi68qmCwoVttjnp7oq0ahg@mail.gmail.com> (raw)
In-Reply-To: <20200703103241.GB182102@jagdpanzerIV.localdomain>

On Fri, Jul 3, 2020 at 1:32 PM Sergey Senozhatsky
<sergey.senozhatsky@gmail.com> wrote:
>
> On (20/07/02 09:05), Tony Lindgren wrote:
> > * Sergey Senozhatsky <sergey.senozhatsky@gmail.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.
>
> This is, basically, an equivalent of
>
> ---
>  drivers/tty/serial/8250/8250_port.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index d64ca77d9cfa..dba7747d2ddd 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2275,6 +2275,7 @@ int serial8250_do_startup(struct uart_port *port)
>
>         if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
>                 unsigned char iir1;
> +
>                 /*
>                  * Test for UARTs that do not reassert THRE when the
>                  * transmitter is idle and the interrupt has already
> @@ -2284,8 +2285,6 @@ 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);
> @@ -2297,8 +2296,6 @@ 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);
>
>                 /*

...which effectively is a revert of

768aec0b5bcc ("serial: 8250: fix shared interrupts issues with SMP and
RT kernels")

-- 
With Best Regards,
Andy Shevchenko