linux-kernel - [PATCH 2/2] printk: fix double printing with earlycon

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Message-Id: <20170301161347.4202-3-aleksey.makarov@linaro.org>
Date:   Wed,  1 Mar 2017 19:13:46 +0300
From:   Aleksey Makarov <aleksey.makarov@...aro.org>
To:     linux-serial@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Aleksey Makarov <aleksey.makarov@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Hurley <peter@...leysoftware.com>,
        Jiri Slaby <jslaby@...e.com>,
        Robin Murphy <robin.murphy@....com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH 2/2] 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 appears twice.

The root cause is that the code traverse 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:

	ttyAMA0 -- from command line
	pl011,mmio,0x87e024000000,115200 -- from SPCR

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@...aro.org>
---
 kernel/printk/printk.c | 52 ++++++++++++++++++++++++++++++--------------------
 1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ed2a9b31f214..92008ae9db3f 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
@@ -2460,37 +2478,29 @@ 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;
 
-			if (_braille_register_console(newcon, c))
-				return;
+		if (_braille_register_console(newcon, c))
+			return;
 
-			if (newcon->setup &&
-			    newcon->setup(newcon, c->options) != 0)
-				break;
-		}
+		if (newcon->setup &&
+		    newcon->setup(newcon, c->options) != 0)
+			break;
 
 		newcon->flags |= CON_ENABLED;
-		if (i == preferred_console) {
-			newcon->flags |= CON_CONSDEV;
-			has_preferred = true;
-		}
 		break;
 	}
 
 	if (!(newcon->flags & CON_ENABLED))
 		return;
 
+	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
-- 
2.11.1