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>

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 82927ca..0605192 100644 (file)
--- 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 */