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[PATCH v5 0/3] printk: fix double printing with earlycon

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  [PATCH v5 0/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-15 11:40 +0100
    [PATCH v6 3/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-17 12:50 +0100
      Re: [PATCH v6 3/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-17 14:50 +0100
    [PATCH v7 3/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-17 14:50 +0100
      Re: [PATCH v7 3/3] printk: fix double printing with earlycon Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-03-20 07:20 +0100
    [PATCH v8 3/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-20 11:10 +0100
      Re: [PATCH v8 3/3] printk: fix double printing with earlycon Petr Mladek <pmladek@suse.com> - 2017-03-27 16:20 +0200
        Re: [PATCH v8 3/3] printk: fix double printing with earlycon Aleksey Makarov <aleksey.makarov@linaro.org> - 2017-03-27 18:30 +0200

#1601256 — [PATCH v5 0/3] 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.

This issue was addressed in the patch [1] but the approach was wrong and
a revert [2] was suggested.

First two patches "printk: fix name/type/scope of preferred_console var" and
"printk: rename selected_console -> preferred_console" were sent some
time ago as one patch "printk: fix name and type of some variables" [3].
They fix name/type/scope of some variables without changing the logic.

The real fix is in the second patch.  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 and don't try to
check for double entries.  Then traverse it in reverse order to be sure that if
the console is preferred then it will be the first matching entry.

v5:
- rewrite 3/3.  Insetead of rearranging the loop, introduce an invariant
  "The last non-braille console is always the preferred one" on the
  entries of the console_cmdline array and don't try to check for double
  entries.  Then traverse it in reverse order to be sure that if the console
  is preferred then it will be the first matching entry.
- add a better explanation from Petr Mladek for 2/3.

v4:
It was not sent upstream due to some problems in implementation of 3/3.
- add some Acked-by: and Reviewed-by: to 1/3 and 2/3
- v2 was closer to the original logic, even though v3 looked 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().  Implement correct sequence:
    1) try to match against preferred_console,
    2) if that fails check other entries of console_cmdline.
  Also move braille console matching/registration to a separate pass to simplify
  the code.

v3 (only for 3/3):
https://lkml.kernel.org/r/20170303154946.15399-1-aleksey.makarov@linaro.org
- v2 still changes the logic of the code and calls newcon->match() several
  times.  V3 fixes that.  It initially matches the console against
  the preferred_console entry, and then if that fails, against other entries.

v2:
https://lkml.kernel.org/r/20170302131153.22733-1-aleksey.makarov@linaro.org
- split the patch that renames `selected_console` and `preferred_console`
  into two patches (Steven Rostedt)
- add a comment explaining why we need a separate match to check for
  preferred_console (Steven Rostedt)
- v1 of this patchset changed the logic of console initialization a bit.
  That could lead to bugs/incompatibilities.  Use the exactly the same
  logic as in the original code.

v1:
https://lkml.kernel.org/r/20170301161347.4202-1-aleksey.makarov@linaro.org

[1] https://lkml.kernel.org/r/1485963998-921-1-git-send-email-sudeep.holla@arm.com
    commit aea9a80ba98a ("tty: serial: pl011: add ttyAMA for matching pl011 console")
[2] https://lkml.kernel.org/r/20170301152304.29635-1-aleksey.makarov@linaro.org
[3] https://lkml.kernel.org/r/1455299022-11641-2-git-send-email-aleksey.makarov@linaro.org

Aleksey Makarov (3):
  printk: fix name/type/scope of preferred_console var
  printk: rename selected_console -> preferred_console
  printk: fix double printing with earlycon

 kernel/printk/printk.c | 61 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 37 insertions(+), 24 deletions(-)

-- 
2.12.0

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#1603232 — [PATCH v6 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, split the loop where we search for matching entry of
console_cmdline into three parts that do not intersect:
1) search for braille console
2) check for preferred_console
3) match other entries so that these three parts do not

To to that introduce predicate _braille_is_braille_console() that checks if
its argument is an entry describing a braille console.

Also introduce a macro for_each_console_cmdline() to traverse
the console_cmdline array.

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---

v5 -> v6:
- drop v5 and continue to work on v4:
- introduce _braille_is_braille_console(). It helps to split original loop
  into three parts: 1) search for braille console, 2) check for
  preferred_console, 3) match other entries so that these three parts do not
  intersect.
- introduce for_each_console_cmdline() macros to traverse console_cmdline
  (Petr Mladek)

 kernel/printk/braille.h |  12 ++++++
 kernel/printk/printk.c  | 104 ++++++++++++++++++++++++++++++++++--------------
 2 files changed, 86 insertions(+), 30 deletions(-)

diff --git a/kernel/printk/braille.h b/kernel/printk/braille.h
index 769d771145c8..183aebf6e1dc 100644
--- a/kernel/printk/braille.h
+++ b/kernel/printk/braille.h
@@ -18,6 +18,12 @@ _braille_register_console(struct console *console, struct console_cmdline *c);
 int
 _braille_unregister_console(struct console *console);
 
+static inline int
+_braille_is_braille_console(struct console_cmdline *c)
+{
+	return !!c->brl_options;
+}
+
 #else
 
 static inline void
@@ -43,6 +49,12 @@ _braille_unregister_console(struct console *console)
 	return 0;
 }
 
+static inline int
+_braille_is_braille_console(struct console_cmdline *c)
+{
+	return 0;
+}
+
 #endif
 
 #endif
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fd752f0c8ef1..ab2433681ca5 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -270,6 +270,11 @@ static struct console *exclusive_console;
 
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
+#define for_each_console_cmdline(i, c)			\
+	for (i = 0, c = console_cmdline;		\
+	     i < MAX_CMDLINECONSOLES && c->name[0];	\
+	     i++, c++)
+
 static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
@@ -1905,9 +1910,7 @@ 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_each_console_cmdline(i, c) {
 		if (strcmp(c->name, name) == 0 && c->index == idx) {
 			if (!brl_options)
 				preferred_console = i;
@@ -2383,6 +2386,37 @@ static int __init keep_bootcon_setup(char *str)
 
 early_param("keep_bootcon", keep_bootcon_setup);
 
+static bool match_console_name(struct console *newcon,
+			       struct console_cmdline *c)
+{
+	BUILD_BUG_ON(sizeof(c->name) != sizeof(newcon->name));
+	if (strcmp(c->name, newcon->name) != 0)
+		return false;
+	if (newcon->index >= 0 && newcon->index != c->index)
+		return false;
+	if (newcon->index < 0)
+		newcon->index = c->index;
+	return true;
+}
+
+static bool match_console(struct console *newcon, struct console_cmdline *c)
+{
+	if (newcon->match &&
+	    newcon->match(newcon, c->name, c->index, c->options) == 0) {
+		newcon->flags |= CON_ENABLED;
+		return true;
+	}
+
+	if (match_console_name(newcon, c)) {
+		if (!newcon->setup || newcon->setup(newcon, c->options) == 0)
+			newcon->flags |= CON_ENABLED;
+
+		return true;
+	}
+
+	return false;
+}
+
 /*
  * The console driver calls this routine during kernel initialization
  * to register the console printing procedure with printk() and to
@@ -2457,40 +2491,50 @@ 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.
+	 * Do it in three steps:
+	 *
+	 * 1) check if it is a braille console..
 	 */
-	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 (_braille_register_console(newcon, c))
-				return;
-
-			if (newcon->setup &&
-			    newcon->setup(newcon, c->options) != 0)
-				break;
-		}
+	for_each_console_cmdline(i, c)
+		if (_braille_is_braille_console(c) &&
+		    match_console_name(newcon, c) &&
+		    _braille_register_console(newcon, c))
+			return;
 
-		newcon->flags |= CON_ENABLED;
-		if (i == preferred_console) {
+	/*
+	 * 2) 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 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
+	 *
+	 * so we can not use the first match.  Instead check the
+	 * entry pointed by preferred_console and then all other entries.
+	 */
+	if (preferred_console >= 0 &&
+	    match_console(newcon, console_cmdline + preferred_console)) {
+		if (newcon->flags & CON_ENABLED) {
 			newcon->flags |= CON_CONSDEV;
 			has_preferred = true;
 		}
-		break;
+		goto match;
+	}
+
+	/*
+	 * 3) check other entries
+	 */
+	for_each_console_cmdline(i, c) {
+		if (preferred_console == i || _braille_is_braille_console(c))
+			continue;
+
+		if (match_console(newcon, c))
+			goto match;
 	}
 
+match:
 	if (!(newcon->flags & CON_ENABLED))
 		return;
 
-- 
2.12.0

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#1603321 — Re: [PATCH v6 3/3] printk: fix double printing with earlycon

On 03/17/2017 02:43 PM, Aleksey Makarov wrote:

[..]

> @@ -2457,40 +2491,50 @@ 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.
> +	 * Do it in three steps:
> +	 *
> +	 * 1) check if it is a braille console..
>  	 */
> -	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 (_braille_register_console(newcon, c))
> -				return;
> -
> -			if (newcon->setup &&
> -			    newcon->setup(newcon, c->options) != 0)
> -				break;
> -		}
> +	for_each_console_cmdline(i, c)
> +		if (_braille_is_braille_console(c) &&
> +		    match_console_name(newcon, c) &&
> +		    _braille_register_console(newcon, c))
> +			return;

I am sorry to say that, but it looks like this does not work either.
newcon->index still can be changed here in match_console_name(), 
but (correctly implemented) _braille_register_console() may refuse
to register it, and the changed newcon is passed to newcon->match() below.

I tried the shuffle (i. e. v5) approach again and it seems I managed to
write quite nice code.  I am going to send it in a minute.

Thank you
Aleksey Makarov

> -		newcon->flags |= CON_ENABLED;
> -		if (i == preferred_console) {
> +	/*
> +	 * 2) 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 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
> +	 *
> +	 * so we can not use the first match.  Instead check the
> +	 * entry pointed by preferred_console and then all other entries.
> +	 */
> +	if (preferred_console >= 0 &&
> +	    match_console(newcon, console_cmdline + preferred_console)) {
> +		if (newcon->flags & CON_ENABLED) {
>  			newcon->flags |= CON_CONSDEV;
>  			has_preferred = true;
>  		}
> -		break;
> +		goto match;
> +	}
> +
> +	/*
> +	 * 3) check other entries
> +	 */
> +	for_each_console_cmdline(i, c) {
> +		if (preferred_console == i || _braille_is_braille_console(c))
> +			continue;
> +
> +		if (match_console(newcon, c))
> +			goto match;
>  	}
>  
> +match:
>  	if (!(newcon->flags & CON_ENABLED))
>  		return;
>  
> 

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#1603322 — [PATCH v7 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.

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---

v6 -> v7:
- return back to v5 :)
- leave the check for already registered entries and add a function that
  maintains the invariant.

v5 -> v6:
- drop v5 and continue to work on v4:
- introduce _braille_is_braille_console(). It helps to split original loop
  into three parts: 1) search for braille console, 2) check for
  preferred_console, 3) match other entries so that these three parts do not
  intersect.
- introduce for_each_console_cmdline() macros to traverse console_cmdline
  (Petr Mladek)

 kernel/printk/printk.c | 48 ++++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fd752f0c8ef1..88f86fb23bc4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1895,6 +1895,34 @@ asmlinkage __visible void early_printk(const char *fmt, ...)
 }
 #endif
 
+/*
+ * This function maintains 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.
+ */
+static void ensure_preferred_is_last(int i)
+{
+	int last;
+
+	for (last = MAX_CMDLINECONSOLES - 1;
+	     last >= 0 && !console_cmdline[last].name[0];
+	     last--)
+		;
+
+	BUG_ON(last < 0);
+
+	if (i != last) {
+		struct console_cmdline t;
+
+		t = console_cmdline[i];
+		console_cmdline[i] = console_cmdline[last];
+		console_cmdline[last] = t;
+	}
+
+	preferred_console = last;
+}
+
 static int __add_preferred_console(char *name, int idx, char *options,
 				   char *brl_options)
 {
@@ -1910,7 +1938,7 @@ 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)
-				preferred_console = i;
+				ensure_preferred_is_last(i);
 			return 0;
 		}
 	}
@@ -2457,12 +2485,20 @@ 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.
+	 *
+	 * The console_cmdline array is traversed in the reverse order because
+	 * we want 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 = MAX_CMDLINECONSOLES - 1; i >= 0; i--) {
+
+		if (!console_cmdline[i].name[0])
+			continue;
+
+		c = console_cmdline + i;
+
 		if (!newcon->match ||
 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
 			/* default matching */
-- 
2.12.0

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#1604192 — Re: [PATCH v7 3/3] printk: fix double printing with earlycon

Hello,

On (03/17/17 16:43), Aleksey Makarov wrote:
[..]
> +static void ensure_preferred_is_last(int i)
> +{
> +	int last;
> +
> +	for (last = MAX_CMDLINECONSOLES - 1;
> +	     last >= 0 && !console_cmdline[last].name[0];
> +	     last--)
> +		;
> +
> +	BUG_ON(last < 0);

let's not panic().


a nitpick, console swap can be done as

	if (i != last)
		swap(console_cmdline[i], console_cmdline[last]);
	preferred_console = last;


		-ss

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#1604324 — [PATCH v8 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.

Reported-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
---

v7 -> v8:
- add an explanation to the comment how console_cmdline can contain entries
  referring to the same console
- move the body of the function introduced in the previous version to cycle
- don't panic() (Sergey Senozhatsky).  Don't check this condition because
  the loop condition guarantees that it holds.
- use swap() (Sergey Senozhatsky)

v6 -> v7:
- return back to v5 
- leave the check for already registered entries and add a function that
  maintains the invariant.

v5 -> v6:
- drop v5 and continue to work on v4:
- introduce _braille_is_braille_console(). It helps to split original loop
  into three parts: 1) search for braille console, 2) check for
  preferred_console, 3) match other entries so that these three parts do not
  intersect.
- introduce for_each_console_cmdline() macros to traverse console_cmdline
  (Petr Mladek)

 kernel/printk/printk.c | 49 ++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 42 insertions(+), 7 deletions(-)

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--)
+				;
+
+			if (i != last)
+				swap(console_cmdline[i], console_cmdline[last]);
+
+			preferred_console = last;
 			return 0;
 		}
 	}
@@ -2457,12 +2477,27 @@ 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 = MAX_CMDLINECONSOLES - 1; i >= 0; i--) {
+
+		if (!console_cmdline[i].name[0])
+			continue;
+
+		c = console_cmdline + i;
+
 		if (!newcon->match ||
 		    newcon->match(newcon, c->name, c->index, c->options) != 0) {
 			/* default matching */
-- 
2.12.0

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#1609877 — Re: [PATCH v8 3/3] printk: fix double printing with earlycon

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

> 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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#1609974 — Re: [PATCH v8 3/3] printk: fix double printing with earlycon

On 03/27/2017 05:14 PM, Petr Mladek wrote:
> On Mon 2017-03-20 13:03:00, Aleksey Makarov wrote:

[..]

>> 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.

Having an additional variable console_cmdline_last pointing to the last element
would require maintaining consistency between this variable and
contents of console_cmdline.  For the code we have it is not hard, but when code
is changed we need to check this.  Also there exists preferred_console that
has almost the same meaning but it points not to the last element, but to the
last non-braille element.  Also we need to have a special value (-1) for this
variable for empty array. So I personally would instead try to rewrite this:

	for (last = MAX_CMDLINECONSOLES - 1; last >= 0; last--)
		if (console_cmdline[last].name[0])
			break;

Is it better?  If not, I will send a version with console_cmdline_last.

>> +
>> +			if (i != last)
>> +				swap(console_cmdline[i], console_cmdline[last]);
>
> I was not aware of the swap() function. It is great to know ;-)

Yes, same for me.  Thanks to Sergey Senozhatsky.

Thank you for review
Aleksey Makarov

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