lkml.org 
[lkml]   [2020]   [Jun]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: UART/TTY console deadlock
On (20/06/30 14:22), Petr Mladek wrote:
> On Tue 2020-06-30 19:55:12, Sergey Senozhatsky wrote:
> > On (20/06/30 12:21), Petr Mladek wrote:
> > > Anyway, I believe that this is a false positive. If I get it correctly
> > > serial8250_do_startup() must be called before the serial port could
> > > be registered as a console. It means that it could not be called
> > > from inside printk().
> >
> > >From my understanding, I'm afraid we are talking about actual deadlock
> > here, not about false positive report. Quoting the original email:
>
> IMHO, it is not clear.
>

Yea. Maybe it is, maybe it's not.

Regardless, after lockdep tells us there is something it doesn't like,
it disables itself, so false positives render lockdep useless.

> > > > @@ -2275,6 +2275,11 @@ int serial8250_do_startup(struct uart_port *port)
> > > >
> > > > if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
> > > > unsigned char iir1;
> > > > + bool irq_shared = up->port.irqflags & IRQF_SHARED;
> > > > +
> > > > + if (irq_shared)
> > > > + disable_irq_nosync(port->irq);
> > > > +
> > > > /*
> > > > * Test for UARTs that do not reassert THRE when the
> > > > * transmitter is idle and the interrupt has already
> > > > @@ -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.

-ss

\
 
 \ /
  Last update: 2020-06-30 15:05    [W:0.106 / U:4.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site