[PATCH 2/2] media: drivers/media/dvb-core: Refactor dvb_frontend_open locking

[Ricardo Ribalda]

Split out the wait function, and introduce some new toys: guard and
lockdep.

This fixes the following cocci warnings:
drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2776
drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2786
drivers/media/dvb-core/dvb_frontend.c:2897:1-7: preceding lock on line 2809

Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
---
 drivers/media/dvb-core/dvb_frontend.c | 59 ++++++++++++++++++++++-------------
 1 file changed, 38 insertions(+), 21 deletions(-)

diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
index e81b9996530e..a7739f5e78cb 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -30,6 +30,7 @@
 #include <linux/kthread.h>
 #include <linux/ktime.h>
 #include <linux/compat.h>
+#include <linux/lockdep.h>
 #include <asm/processor.h>
 
 #include <media/dvb_frontend.h>
@@ -2826,6 +2827,34 @@ static int __dvb_frontend_open(struct inode *inode, struct file *file)
 	return ret;
 }
 
+static int wait_dvb_frontend(struct dvb_adapter *adapter,
+			       struct dvb_device *mfedev)
+{
+	struct dvb_frontend *mfe = mfedev->priv;
+	struct dvb_frontend_private *mfepriv = mfe->frontend_priv;
+	int mferetry = (dvb_mfe_wait_time << 1);
+	int ret = 0;
+
+	lockdep_assert_held(&adapter->mfe_lock);
+
+	if (mfedev->users == -1 && !mfepriv->thread)
+		return 0;
+
+	mutex_unlock(&adapter->mfe_lock);
+
+	while (mferetry-- && (mfedev->users != -1 || mfepriv->thread)) {
+		if (msleep_interruptible(500))
+			if (signal_pending(current)) {
+				ret = -EINTR;
+				break;
+			}
+	}
+
+	mutex_lock(&adapter->mfe_lock);
+
+	return ret;
+}
+
 static int dvb_frontend_open(struct inode *inode, struct file *file)
 {
 	struct dvb_device *dvbdev = file->private_data;
@@ -2840,19 +2869,17 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 	if (!adapter->mfe_shared)
 		return __dvb_frontend_open(inode, file);
 
+
+	guard(mutex)(&adapter->mfe_lock);
+
 	if (adapter->mfe_shared == 2) {
-		mutex_lock(&adapter->mfe_lock);
 		if ((file->f_flags & O_ACCMODE) != O_RDONLY) {
 			if (adapter->mfe_dvbdev &&
-			    !adapter->mfe_dvbdev->writers) {
-				mutex_unlock(&adapter->mfe_lock);
+			    !adapter->mfe_dvbdev->writers)
 				return -EBUSY;
-			}
 			adapter->mfe_dvbdev = dvbdev;
 		}
 	} else {
-		mutex_lock(&adapter->mfe_lock);
-
 		if (!adapter->mfe_dvbdev) {
 			adapter->mfe_dvbdev = dvbdev;
 		} else if (adapter->mfe_dvbdev != dvbdev) {
@@ -2862,34 +2889,24 @@ static int dvb_frontend_open(struct inode *inode, struct file *file)
 				*mfe = mfedev->priv;
 			struct dvb_frontend_private
 				*mfepriv = mfe->frontend_priv;
-			int mferetry = (dvb_mfe_wait_time << 1);
-
-			mutex_unlock(&adapter->mfe_lock);
-			while (mferetry-- && (mfedev->users != -1 ||
-					      mfepriv->thread)) {
-				if (msleep_interruptible(500)) {
-					if (signal_pending(current))
-						return -EINTR;
-				}
-			}
 
-			mutex_lock(&adapter->mfe_lock);
+			ret = wait_dvb_frontend(adapter, mfedev);
+			if (ret)
+				return ret;
+
 			if (adapter->mfe_dvbdev != dvbdev) {
 				mfedev = adapter->mfe_dvbdev;
 				mfe = mfedev->priv;
 				mfepriv = mfe->frontend_priv;
 				if (mfedev->users != -1 ||
-				    mfepriv->thread) {
-					mutex_unlock(&adapter->mfe_lock);
+				    mfepriv->thread)
 					return -EBUSY;
-				}
 				adapter->mfe_dvbdev = dvbdev;
 			}
 		}
 	}
 
 	ret = __dvb_frontend_open(inode, file);
-	mutex_unlock(&adapter->mfe_lock);
 
 	return ret;
 }

-- 
2.45.2.505.gda0bf45e8d-goog