Subject: [PATCH] tty/hvc/hvc_console: Fix wakeup of HVC thread on hvc_kick()

From: Benjamin Herrenschmidt <[email-masked]>
Date: Fri, 23 May 2014 19:41:06 +1000

Some backends call hvc_kick() to wakeup the HVC thread from its
slumber upon incoming characters. This however doesn't work
properly because it uses msleep_interruptible() which is mostly
immune to wake_up_process(). It will basically go back to sleep
until the timeout is expired (only signals can really wake it).

Replace it with a simple shedule_timeout_interruptible() instead,
which may wakeup earlier every now and then but we really don't
care in this case.

Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
---
 drivers/tty/hvc/hvc_console.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c
index 94f9e3a..1094265 100644
--- a/drivers/tty/hvc/hvc_console.c
+++ b/drivers/tty/hvc/hvc_console.c
@@ -760,10 +760,17 @@ static int khvcd(void *unused)
 			if (poll_mask == 0)
 				schedule();
 			else {
+				unsigned long j_timeout;
+
 				if (timeout < MAX_TIMEOUT)
 					timeout += (timeout >> 6) + 1;
 
-				msleep_interruptible(timeout);
+				/*
+				 * We don't use msleep_interruptible otherwise
+				 * "kick" will fail to wake us up
+				 */
+				j_timeout = msecs_to_jiffies(timeout) + 1;
+				schedule_timeout_interruptible(j_timeout);
 			}
 		}
 		__set_current_state(TASK_RUNNING);