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

From: Byeong-ki Shin
Date: Thu Jan 15 2015 - 01:14:10 EST


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

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