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

Aleksey Makarov
2017-03-02T13:11:34Z

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 {

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
--
2.11.1