printk: fix double printing with earlycon

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.

Link: http://lkml.kernel.org/r/20170405202006.18234-1-aleksey.makarov@linaro.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

1 files changed, 36 insertions, 10 deletions

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82927ca04849..06051926dfde 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -266,6 +266,7 @@ 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;
@@ -1902,12 +1903,25 @@ 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;
+                        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;
                 }
         }
@@ -1920,6 +1934,7 @@ static int __add_preferred_console(char *name, int idx, char *options,
         braille_set_options(c, brl_options);
 
         c->index = idx;
+        console_cmdline_cnt++;
         return 0;
 }
 /*
@@ -2459,12 +2474,23 @@ 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--) {
+                c = console_cmdline + i;
+
                 if (!newcon->match ||
                     newcon->match(newcon, c->name, c->index, c->options) != 0) {
                         /* default matching */