Re: [PATCH v9 3/3] printk: fix double printing with earlycon

[Aleksey Makarov]

On 04/10/2017 05:22 PM, Petr Mladek wrote:
> On Wed 2017-04-05 23:20:00, Aleksey Makarov wrote:
> > If a console was specified by ACPI SPCR table _and_ command line
> > parameters like "console=ttyAMA0" _and_ "earlycon" were specified,
> > then log messages appear twice.
> >
> > The root cause is that the code traverses the list of specified
> > consoles (the `console_cmdline` array) and stops at the first match.
> > But it may happen that the same console is referred by the elements
> > of this array twice:
> >
> > 	pl011,mmio,0x87e024000000,115200 -- from SPCR
> > 	ttyAMA0 -- from command line
> >
> > but in this case `preferred_console` points to the second entry and
> > the flag CON_CONSDEV is not set, so bootconsole is not deregistered.
> >
> > To fix that, introduce an invariant "The last non-braille console
> > is always the preferred one" on the entries of the console_cmdline
> > array.  Then traverse it in reverse order to be sure that if
> > the console is preferred then it will be the first matching entry.
> > Introduce variable console_cmdline_cnt that keeps the number
> > of elements of the console_cmdline array (Petr Mladek).  It helps
> > to get rid of the loop that searches for the end of this array.
> >
> > Reported-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> > Signed-off-by: Aleksey Makarov <aleksey.makarov@xxxxxxxxxx>
>
> This version looks fine to me. Just a small nitpick below.
> Anyway:
>
> Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>

Thank you for review.  Can you (or anybody else) ACK it?
I am going to resend the whole series without those empty lines.
May I add your Acked-by:?

Thank you
Aleksey Makarov

> > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> > index fd752f0c8ef1..be657af45758 100644
> > --- a/kernel/printk/printk.c
> > +++ b/kernel/printk/printk.c
> > @@ -269,6 +269,7 @@ static struct console *exclusive_console;
> >   #define MAX_CMDLINECONSOLES 8
> >   
> >   static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
> > +static int console_cmdline_cnt;
> >   
> >   static int preferred_console = -1;
> >   int console_set_on_cmdline;
> > @@ -1905,12 +1906,26 @@ static int __add_preferred_console(char *name, int idx, char *options,
> >   	 *	See if this tty is not yet registered, and
> >   	 *	if we have a slot free.
> >   	 */
> > -	for (i = 0, c = console_cmdline;
> > -	     i < MAX_CMDLINECONSOLES && c->name[0];
> > -	     i++, c++) {
> > +	for (i = 0, c = console_cmdline; i < console_cmdline_cnt; i++, c++) {
> >   		if (strcmp(c->name, name) == 0 && c->index == idx) {
> > -			if (!brl_options)
> > -				preferred_console = i;
> > +
>
> This extra new line is non-standard and looks slightly weird to me.
> I just point it out. I personally do not mind ;-)
>
>
> > +			if (brl_options)
> > +				return 0;
> > +
> > +			/*
> > +			 * Maintain an invariant that will help to find if
> > +			 * the matching console is preferred, see
> > +			 * register_console():
> > +			 *
> > +			 * The last non-braille console is always
> > +			 * the preferred one.
> > +			 */
> > +			if (i != console_cmdline_cnt - 1)
> > +				swap(console_cmdline[i],
> > +				     console_cmdline[console_cmdline_cnt - 1]);
> > +
> > +			preferred_console = console_cmdline_cnt - 1;
> > +
> >   			return 0;
> >   		}
> >   	}
> > @@ -2457,12 +2473,24 @@ void register_console(struct console *newcon)
> >   	}
> >   
> >   	/*
> > -	 *	See if this console matches one we selected on
> > -	 *	the command line.
> > +	 * See if this console matches one we selected on the command line.
> > +	 *
> > +	 * There may be several entries in the console_cmdline array matching
> > +	 * with the same console, one with newcon->match(), another by
> > +	 * name/index:
> > +	 *
> > +	 *	pl011,mmio,0x87e024000000,115200 -- added from SPCR
> > +	 *	ttyAMA0 -- added from command line
> > +	 *
> > +	 * Traverse the console_cmdline array in reverse order to be
> > +	 * sure that if this console is preferred then it will be the first
> > +	 * matching entry.  We use the invariant that is maintained in
> > +	 * __add_preferred_console().
> >   	 */
> > -	for (i = 0, c = console_cmdline;
> > -	     i < MAX_CMDLINECONSOLES && c->name[0];
> > -	     i++, c++) {
> > +	for (i = console_cmdline_cnt - 1; i >= 0; i--) {
> > +
>
> Same here.
>
> > +		c = console_cmdline + i;
> > +
> >   		if (!newcon->match ||
> >   		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
> >   			/* default matching */
>
> Best Regards,
> Petr