[printk] fix double printing with earlycon

[printk] fix double printing with earlycon

[Sergey Senozhatsky]

[-- Attachment #1: Type: text/plain, Size: 544 bytes --]

Hello Fengguang, Xiaolong

I've noticed that the serial output you sometimes provide has repeating
lines (double lines). Is this intentional? we are about to push a patch
set to the linux-next that fixes "double printing" issue and I'm wondering
will it break anything on your side. Can you please test it?

1/3  https://marc.info/?l=linux-kernel&m=148957402019729&w=2
2/3  https://marc.info/?l=linux-kernel&m=148957403319736&w=2
3/3  https://marc.info/?l=linux-kernel&m=149142366508431&w=2

I've also attached the patches.

	-ss

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: 0001-printk-fix-name-type-scope-of-preferred_console-var.patch --]
[-- Type: text/x-diff, Size: 2596 bytes --]

>From 68a432d0f48243eab14f19aefa93b1a6194121d5 Mon Sep 17 00:00:00 2001
From: Aleksey Makarov <aleksey.makarov@linaro.org>
Date: Wed, 15 Mar 2017 13:28:50 +0300
Subject: [PATCH 1/3] printk: fix name/type/scope of preferred_console var

The variable preferred_console is used only inside register_console()
and its semantics is boolean.  It is negative when no console has been
made preferred.

Make it static bool and rename to has_preferred.

Renaming was suggested by Peter Hurley

Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---
 kernel/printk/printk.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2984fb0f0257..80bc1b72d03d 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -271,7 +271,6 @@ static struct console *exclusive_console;
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
 static int selected_console = -1;
-static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
@@ -2409,6 +2408,7 @@ void register_console(struct console *newcon)
 	unsigned long flags;
 	struct console *bcon = NULL;
 	struct console_cmdline *c;
+	static bool has_preferred;
 
 	if (console_drivers)
 		for_each_console(bcon)
@@ -2435,15 +2435,15 @@ void register_console(struct console *newcon)
 	if (console_drivers && console_drivers->flags & CON_BOOT)
 		bcon = console_drivers;
 
-	if (preferred_console < 0 || bcon || !console_drivers)
-		preferred_console = selected_console;
+	if (!has_preferred || bcon || !console_drivers)
+		has_preferred = selected_console >= 0;
 
 	/*
 	 *	See if we want to use this console driver. If we
 	 *	didn't select a console we take the first one
 	 *	that registers here.
 	 */
-	if (preferred_console < 0) {
+	if (!has_preferred) {
 		if (newcon->index < 0)
 			newcon->index = 0;
 		if (newcon->setup == NULL ||
@@ -2451,7 +2451,7 @@ void register_console(struct console *newcon)
 			newcon->flags |= CON_ENABLED;
 			if (newcon->device) {
 				newcon->flags |= CON_CONSDEV;
-				preferred_console = 0;
+				has_preferred = true;
 			}
 		}
 	}
@@ -2486,7 +2486,7 @@ void register_console(struct console *newcon)
 		newcon->flags |= CON_ENABLED;
 		if (i == selected_console) {
 			newcon->flags |= CON_CONSDEV;
-			preferred_console = selected_console;
+			has_preferred = true;
 		}
 		break;
 	}
-- 
2.12.2


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #3: 0002-printk-rename-selected_console-preferred_console.patch --]
[-- Type: text/x-diff, Size: 2733 bytes --]

>From d2a59b52dd1e2167219a10d0d1e850da72d5e7cf Mon Sep 17 00:00:00 2001
From: Aleksey Makarov <aleksey.makarov@linaro.org>
Date: Wed, 15 Mar 2017 13:28:51 +0300
Subject: [PATCH 2/3] printk: rename selected_console -> preferred_console

The variable selected_console is set in __add_preferred_console()
to point to the last console parameter that was added to the
console_cmdline array.

Rename it to preferred_console so that the name reflects the usage.

Petr Mladek:
"[..] the selected_console/preferred_console
value is used to keep the console first in the console_drivers list.
IMHO, the main effect is that each line will first appear on this
console, see call_console_drivers(). But the message will still
appear also on all other enabled consoles. From this point,
the name "preferred" sounds better to me. More consoles
are selected (enabled) and only one is preferred (first)."

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Suggested-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---
 kernel/printk/printk.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 80bc1b72d03d..fd752f0c8ef1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -270,7 +270,7 @@ static struct console *exclusive_console;
 
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
-static int selected_console = -1;
+static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
@@ -1910,14 +1910,14 @@ static int __add_preferred_console(char *name, int idx, char *options,
 	     i++, c++) {
 		if (strcmp(c->name, name) == 0 && c->index == idx) {
 			if (!brl_options)
-				selected_console = i;
+				preferred_console = i;
 			return 0;
 		}
 	}
 	if (i == MAX_CMDLINECONSOLES)
 		return -E2BIG;
 	if (!brl_options)
-		selected_console = i;
+		preferred_console = i;
 	strlcpy(c->name, name, sizeof(c->name));
 	c->options = options;
 	braille_set_options(c, brl_options);
@@ -2436,7 +2436,7 @@ void register_console(struct console *newcon)
 		bcon = console_drivers;
 
 	if (!has_preferred || bcon || !console_drivers)
-		has_preferred = selected_console >= 0;
+		has_preferred = preferred_console >= 0;
 
 	/*
 	 *	See if we want to use this console driver. If we
@@ -2484,7 +2484,7 @@ void register_console(struct console *newcon)
 		}
 
 		newcon->flags |= CON_ENABLED;
-		if (i == selected_console) {
+		if (i == preferred_console) {
 			newcon->flags |= CON_CONSDEV;
 			has_preferred = true;
 		}
-- 
2.12.2


[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #4: 0003-printk-fix-double-printing-with-earlycon.patch --]
[-- Type: text/x-diff, Size: 4101 bytes --]

>From d2a0dffbffa18f0022544132637552e5bc69e8e1 Mon Sep 17 00:00:00 2001
From: Aleksey Makarov <aleksey.makarov@linaro.org>
Date: Wed, 5 Apr 2017 23:20:00 +0300
Subject: [PATCH 3/3] 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.

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---
 kernel/printk/printk.c | 48 ++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 38 insertions(+), 10 deletions(-)

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;
+
+			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;
 		}
 	}
@@ -1923,6 +1938,7 @@ 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;
 }
 /*
@@ -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--) {
+
+		c = console_cmdline + i;
+
 		if (!newcon->match ||
 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
 			/* default matching */
-- 
2.12.2