On Mon 2017-03-20 13:03:00, 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.
Sigh, I am afraid that we need to go this way. I hate the side
effects of the match() functions. It would be great to get
rid of them. But it is non-trivial and out of scope for this fix.
> Reported-by: Sudeep Holla <sudeep.holla@xxxxxxx>
> Signed-off-by: Aleksey Makarov <aleksey.makarov@xxxxxxxxxx>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index fd752f0c8ef1..462036e7a767 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1909,8 +1909,28 @@ static int __add_preferred_console(char *name, int idx, char *options,
> i < MAX_CMDLINECONSOLES && c->name[0];
> i++, c++) {
> if (strcmp(c->name, name) == 0 && c->index == idx) {
> - if (!brl_options)
> - preferred_console = i;
> + int last;
> +
> + 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.
> + */
> + for (last = MAX_CMDLINECONSOLES - 1;
> + last >= 0 && !console_cmdline[last].name[0];
> + last--)
> + ;
This is a rather non-trivial code to find the last element.
I might make sense to count it in a global variable.
Then we might remove the check for console_cmdline[i].name[0]
also in the other for cycles and make them better readable.
> +
> + if (i != last)
> + swap(console_cmdline[i], console_cmdline[last]);
I was not aware of the swap() function. It is great to know ;-)
Otherwise, I am find with this approach.
Best Regards,
Petr
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