[PATCH v3 3/3] printk: fix double printing with earlycon

Aleksey Makarov
2017-03-03T15:49:41Z

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` and if that fails, match against other
entries. The problem is that newcon->match() is not just a match
function, it calls setup() so it has side effects.

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

v2 -> v3:

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.

kernel/printk/printk.c | 82 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 59 insertions(+), 23 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ed2a9b31f214..99bea4ae8f4a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2380,6 +2380,32 @@ static int __init keep_bootcon_setup(char *str)

early_param("keep_bootcon", keep_bootcon_setup);

+static enum { CONSOLE_MATCH, CONSOLE_MATCH_RETURN, CONSOLE_MATCH_NEXT }
+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 CONSOLE_MATCH_NEXT;
+ if (newcon->index >= 0 && newcon->index != c->index)
+ return CONSOLE_MATCH_NEXT;
+ if (newcon->index < 0)
+ newcon->index = c->index;
+
+ if (_braille_register_console(newcon, c))
+ return CONSOLE_MATCH_RETURN;
+
+ if (newcon->setup &&
+ newcon->setup(newcon, c->options) != 0)
+ return CONSOLE_MATCH;
+ }
+
+ newcon->flags |= CON_ENABLED;
+ return CONSOLE_MATCH;
+}
+
/*
* The console driver calls this routine during kernel initialization
* to register the console printing procedure with printk() and to
@@ -2454,40 +2480,50 @@ void register_console(struct console *newcon)
}

/*
+ * 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 so we
+ * can not just use the first match. Instead check the entry pointed
+ * by preferred_console and then all other entries.
+ */
+ if (preferred_console >= 0) {
+ switch (match_console(newcon,
+ console_cmdline + preferred_console)) {
+ case CONSOLE_MATCH:
+ if (newcon->flags | CON_ENABLED) {
+ newcon->flags |= CON_CONSDEV;
+ has_preferred = true;
+ }
+ goto match;
+ case CONSOLE_MATCH_RETURN:
+ return;
+ default:
+ break;
+ }
+ }
+
+ /*
* See if this console matches one we selected on
* the command line.
*/
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;
- }
+ if (preferred_console == i)
+ continue;

- newcon->flags |= CON_ENABLED;
- if (i == preferred_console) {
- newcon->flags |= CON_CONSDEV;
- has_preferred = true;
+ switch (match_console(newcon, c)) {
+ case CONSOLE_MATCH:
+ goto match;
+ case CONSOLE_MATCH_RETURN:
+ return;
+ default:
+ break;
}
- break;
}

+match:
if (!(newcon->flags & CON_ENABLED))
return;

--
2.11.1