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Subject[PATCH] Wait for console to become available
Work to improve boot times appears to be successful enough that a race
condition has been created between the open of /dev/console in init_post
and USB serial device initialization. Embedded systems are probably the
primary users of USB serial devices, though I can certainly image blade
servers using them, as well.

This patch works for me and, though it's possible this is all that needs
to be done, I think it's likely there are some other changes required,
as well.

Signed-off-by: David VomLehn <dvomlehn@cisco>
---
kernel/printk.c | 9 +++++++++
1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index e3602d0..39f554a 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -104,6 +104,10 @@ static unsigned log_start; /* Index into log_buf: next char to be read by syslog
static unsigned con_start; /* Index into log_buf: next char to be sent to consoles */
static unsigned log_end; /* Index into log_buf: most-recently-written-char + 1 */

+/* Definitions for waiting until a console is registered */
+#define MAX_CONSOLE_WAIT msecs_to_jiffies(2000)
+static DECLARE_WAIT_QUEUE_HEAD(console_wait);
+
/*
* Array of consoles built from command line options (console=)
*/
@@ -1062,6 +1066,10 @@ struct tty_driver *console_device(int *index)
struct console *c;
struct tty_driver *driver = NULL;

+ /* Wait a while for a console to show up. If one doesn't show up
+ * for too long, we'll just continue without a console. */
+ wait_event_timeout(console_wait, console_drivers, MAX_CONSOLE_WAIT);
+
acquire_console_sem();
for (c = console_drivers; c != NULL; c = c->next) {
if (!c->device)
@@ -1211,6 +1219,7 @@ void register_console(struct console *console)
spin_unlock_irqrestore(&logbuf_lock, flags);
}
release_console_sem();
+ wake_up_all(&console_wait);
}
EXPORT_SYMBOL(register_console);


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