linux-kernel - Re: [PATCH] uart:8250: change lock order in serial8250_do

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Message-ID: <20200814112940.GB582@jagdpanzerIV.localdomain>
Date:   Fri, 14 Aug 2020 20:29:40 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Tony Lindgren <tony@...mide.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Raul Rangel <rrangel@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH] uart:8250: change lock order in serial8250_do_startup()

On (20/08/14 12:59), Andy Shevchenko wrote:
> > ---
> >  drivers/tty/serial/8250/8250_port.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> > index 09475695effd..67f1a4f31093 100644
> > --- a/drivers/tty/serial/8250/8250_port.c
> > +++ b/drivers/tty/serial/8250/8250_port.c
> > @@ -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;
> 
> I'm wondering why we need a temporary variable? This flag is not supposed to be
> changed in between, can we leave original conditionals?

No particular reason. We can keep the original (long) ones, I guess.

> Nevertheless I noticed an inconsistency of the dereference of the flags which
> seems to be brough by dfe42443ea1d ("serial: reduce number of indirections in
> 8250 code").
>
> I think we can stick with newer:
>
> 		if (port->irqflags & IRQF_SHARED)

I'll take a look.

	-ss