[v2,3/3] printk: fix double printing with earlycon

Message ID 20170302131153.22733-4-aleksey.makarov@linaro.org
State New
Headers show
Series
  • printk: fix double printing with earlycon
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Commit Message

Aleksey Makarov March 2, 2017, 1:11 p.m.
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, match the console against the `console_cmdline` entry
pointed by `preferred_console` instead of the first match.

Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>

---
 kernel/printk/printk.c | 49 ++++++++++++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 15 deletions(-)

-- 
2.11.1

Comments

Aleksey Makarov March 2, 2017, 1:58 p.m. | #1
On 03/02/2017 04:11 PM, 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, match the console against the `console_cmdline` entry

> pointed by `preferred_console` instead of the first match.

> 

> Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>

> ---

>  kernel/printk/printk.c | 49 ++++++++++++++++++++++++++++++++++---------------

>  1 file changed, 34 insertions(+), 15 deletions(-)

> 

> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c

> index ed2a9b31f214..ad35011f8374 100644

> --- a/kernel/printk/printk.c

> +++ b/kernel/printk/printk.c

> @@ -2380,6 +2380,24 @@ static int __init keep_bootcon_setup(char *str)

>  

>  early_param("keep_bootcon", keep_bootcon_setup);

>  

> +static int match_console(struct console *newcon, struct console_cmdline *c)

> +{

> +	if (!newcon->match ||

> +	    newcon->match(newcon, c->name, c->index, c->options) != 0) {

> +		/* default matching */

> +		BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));

> +		if (strcmp(c->name, newcon->name) != 0)

> +			return -ENODEV;

> +		if (newcon->index >= 0 &&

> +		    newcon->index != c->index)

> +			return -ENODEV;

> +		if (newcon->index < 0)

> +			newcon->index = c->index;

> +	}

> +

> +	return 0;

> +}

> +

>  /*

>   * The console driver calls this routine during kernel initialization

>   * to register the console printing procedure with printk() and to

> @@ -2460,17 +2478,9 @@ void register_console(struct console *newcon)

>  	for (i = 0, c = console_cmdline;

>  	     i < MAX_CMDLINECONSOLES && c->name[0];

>  	     i++, c++) {

> -		if (!newcon->match ||

> -		    newcon->match(newcon, c->name, c->index, c->options) != 0) {

> -			/* default matching */

> -			BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));

> -			if (strcmp(c->name, newcon->name) != 0)

> -				continue;

> -			if (newcon->index >= 0 &&

> -			    newcon->index != c->index)

> -				continue;

> -			if (newcon->index < 0)

> -				newcon->index = c->index;

> +		if (match_console(newcon, c)) {

> +			continue;

> +		} else {


My bad.  The first version of this patch was closer to the original logic,
despite this patch looks simpler.

The problem is that newcon->setup() is called twice, firstly from
newcon->match(), then explicitly.  And it could be called third time later 
in another call to newcon->match().

The correct sequence is 1) try to match against preferred_console,
2) if that fails check other entries of console_cmdline.  That would require
some work so I will send a correction tomorrow.

All the best
Aleksey Makarov

Patch

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ed2a9b31f214..ad35011f8374 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2380,6 +2380,24 @@  static int __init keep_bootcon_setup(char *str)
 
 early_param("keep_bootcon", keep_bootcon_setup);
 
+static int match_console(struct console *newcon, struct console_cmdline *c)
+{
+	if (!newcon->match ||
+	    newcon->match(newcon, c->name, c->index, c->options) != 0) {
+		/* default matching */
+		BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
+		if (strcmp(c->name, newcon->name) != 0)
+			return -ENODEV;
+		if (newcon->index >= 0 &&
+		    newcon->index != c->index)
+			return -ENODEV;
+		if (newcon->index < 0)
+			newcon->index = c->index;
+	}
+
+	return 0;
+}
+
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to
@@ -2460,17 +2478,9 @@  void register_console(struct console *newcon)
 	for (i = 0, c = console_cmdline;
 	     i < MAX_CMDLINECONSOLES && c->name[0];
 	     i++, c++) {
-		if (!newcon->match ||
-		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
-			/* default matching */
-			BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
-			if (strcmp(c->name, newcon->name) != 0)
-				continue;
-			if (newcon->index >= 0 &&
-			    newcon->index != c->index)
-				continue;
-			if (newcon->index < 0)
-				newcon->index = c->index;
+		if (match_console(newcon, c)) {
+			continue;
+		} else {
 
 			if (_braille_register_console(newcon, c))
 				return;
@@ -2481,10 +2491,6 @@  void register_console(struct console *newcon)
 		}
 
 		newcon->flags |= CON_ENABLED;
-		if (i == preferred_console) {
-			newcon->flags |= CON_CONSDEV;
-			has_preferred = true;
-		}
 		break;
 	}
 
@@ -2492,6 +2498,19 @@  void register_console(struct console *newcon)
 		return;
 
 	/*
+	 * Check if this console was set as preferred by command line parameters
+	 * or by call to add_preferred_console().
+	 * There may be several entries in the console_cmdline array referring
+	 * to the same console so we can not just use the first match.  Instead
+	 * check the entry pointed by preferred_console explicitly.
+	 */
+	if (preferred_console >= 0 &&
+	    match_console(newcon, console_cmdline + preferred_console) == 0) {
+		newcon->flags |= CON_CONSDEV;
+		has_preferred = true;
+	}
+
+	/*
 	 * If we have a bootconsole, and are switching to a real console,
 	 * don't print everything out again, since when the boot console, and
 	 * the real console are the same physical device, it's annoying to