[PATCH] dvb: core: fix race condition in FE_READ_STATUS ioctl

Fix a race condition where an application which issued a FE_READ_STATUS ioctl
directly after FE_SET_FRONTEND would see an old status, i.e.  FE_READ_STATUS
would be executed before the frontend thread has even seen the tungin request
from FE_SET_FRONTEND.
Signed-off-by: NPeter Beutner <p.beutner@gmx.net>
Signed-off-by: NJohannes Stezenbach <js@linuxtv.org>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

drivers/media/dvb/dvb-core/dvb_frontend.c

@@ -626,11 +626,21 @@ static int dvb_frontend_ioctl(struct inode *inode, struct file *file,
 		break;
 	}
 
-	case FE_READ_STATUS:
+	case FE_READ_STATUS: {
+		fe_status_t* status = parg;
+
+		/* if retune was requested but hasn't occured yet, prevent
+		 * that user get signal state from previous tuning */
+		if(fepriv->state == FESTATE_RETUNE) {
+			err=0;
+			*status = 0;
+			break;
+		}
+
 		if (fe->ops->read_status)
-			err = fe->ops->read_status(fe, (fe_status_t*) parg);
+			err = fe->ops->read_status(fe, status);
 		break;
-
+	}
 	case FE_READ_BER:
 		if (fe->ops->read_ber)
 			err = fe->ops->read_ber(fe, (__u32*) parg);