linux-kernel - Re: UART/TTY console deadlock

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Date:   Fri, 3 Jul 2020 19:32:41 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        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 (20/07/02 09:05), Tony Lindgren wrote:
> * 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.

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);
 
 		/*
-- 
2.27.0