[PATCH] [media] dvb-core: Fix frontend thread serialization

[Byeong-ki Shin <bk0121.shin@xxxxxxxxxxx>]

From 2384c119d04b54e6e6c282a8693246c4e7d1347e Mon Sep 17 00:00:00 2001
From: "bk0121.shin" <bk0121.shin@xxxxxxxxxxx>
Date: Wed, 14 Jan 2015 20:35:57 +0900
Subject: [PATCH] [media] dvb-core: Fix frontend thread serialization

dvb_frontend_thread's life cycle is controlled by dvb_frontend_start
and dvb_frontend_release.
But, if user opens frontend device before the thread exits completely,
dvb_frontend_start doesn't create a new thread.

When exit condition of thread that is jiffies is triggered
by dvb_frontend_release, dvb_frontend_thread wakes up and checks
exit condition without semaphore acquiring.
In this case, if user context checks existence of thread(fepriv->thread),
it is true, and exit flage has DVB_FE_NO_EXIT.
Therefore, dvb_frontend_start doesn't make a new thread,
previous old thread is going to terminate.

To fix this problem, semaphore should preserve thread exit condition and
checking it, which are dvb_frontend_is_exiting and fe->exit.

Signed-off-by: bk0121.shin <bk0121.shin@xxxxxxxxxxx>
---
 drivers/media/dvb-core/dvb_frontend.c | 22 +++++++++++++++-------
 1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index 2cf3057..a8e8d44 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -620,14 +620,17 @@ restart:
 				|| freezing(current),
 			fepriv->delay);
 
+		if (down_interruptible(&fepriv->sem))
+			break;
+
 		if (kthread_should_stop() || dvb_frontend_is_exiting(fe)) {
 			/* got signal or quitting */
-			if (!down_interruptible(&fepriv->sem))
-				semheld = true;
+			semheld = true;
 			fe->exit = DVB_FE_NORMAL_EXIT;
 			break;
 		}
 
+		up(&fepriv->sem);
 		if (try_to_freeze())
 			goto restart;
 
@@ -821,17 +824,22 @@ static int dvb_frontend_start(struct dvb_frontend *fe)
 
 	dev_dbg(fe->dvb->device, "%s:\n", __func__);
 
+	if (down_interruptible(&fepriv->sem))
+		return -EINTR;
+
 	if (fepriv->thread) {
-		if (fe->exit == DVB_FE_NO_EXIT)
+		if (fe->exit == DVB_FE_NO_EXIT) {
+			up(&fepriv->sem);
 			return 0;
-		else
+		} else {
 			dvb_frontend_stop (fe);
+		}
 	}
 
-	if (signal_pending(current))
-		return -EINTR;
-	if (down_interruptible (&fepriv->sem))
+	if (signal_pending(current)) {
+		up(&fepriv->sem);
 		return -EINTR;
+	}
 
 	fepriv->state = FESTATE_IDLE;
 	fe->exit = DVB_FE_NO_EXIT;
-- 
1.9.1





---------------------------------------
Byeongki Shin 
Senior Engineer 

Office:
Mobile: +82-10-3268-8201
E-Mail: bk0121.shin@xxxxxxxxxxx

Attachment: 0001-media-dvb-core-Fix-frontend-thread-serialization.patch
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