0012-tty-n_r3964-remove-read_lock-from-some-ioctls.patch

From 3e1d022e31e12398690f4f8638453b3929fa73d4 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: Fri, 25 Jan 2019 15:20:31 +0100
Subject: [PATCH 12/15] tty: n_r3964: remove read_lock from some ioctls

Now that read_telegram() properly grabs the needed locks for its
operation, we can move the "heavy" read lock away from all ioctls except
one, the R3964_ENABLE_SIGNALS lock.

When we move this lock away, properly grab the info->lock for the other
ioctls that need it so that they will not have any problems.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/n_r3964.c |   28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

--- a/drivers/tty/n_r3964.c
+++ b/drivers/tty/n_r3964.c
@@ -175,7 +175,8 @@ struct r3964_info {
 	unsigned char bcc;
 	unsigned int blocks_in_rx_queue;
 
-	struct mutex read_lock;		/* serialize read and ioctl */
+	/* serialize read and R3964_ENABLE_SIGNALS ioctl */
+	struct mutex read_lock;
 
 	struct list_head clients;
 	unsigned int state;
@@ -1219,33 +1220,41 @@ static int r3964_ioctl(struct tty_struct
 		unsigned int cmd, unsigned long arg)
 {
 	struct r3964_info *pInfo = tty->disc_data;
+	unsigned long flags;
 	int retval = 0;
 
 	if (pInfo == NULL)
 		return -EINVAL;
-	/* Internal serialization of reads and ioctls */
-	if (file->f_flags & O_NONBLOCK) {
-		if (!mutex_trylock(&pInfo->read_lock))
-			return -EAGAIN;
-	} else {
-		if (mutex_lock_interruptible(&pInfo->read_lock))
-			return -ERESTARTSYS;
-	}
 
 	switch (cmd) {
 	case R3964_ENABLE_SIGNALS:
+		/* Internal serialization of reads and this ioctl */
+		if (file->f_flags & O_NONBLOCK) {
+			if (!mutex_trylock(&pInfo->read_lock))
+				return -EAGAIN;
+		} else {
+			if (mutex_lock_interruptible(&pInfo->read_lock))
+				return -ERESTARTSYS;
+		}
+
 		retval = enable_signals(pInfo, task_pid(current), arg);
+
+		mutex_unlock(&pInfo->read_lock);
 		break;
 	case R3964_SETPRIORITY:
 		if (arg < R3964_MASTER || arg > R3964_SLAVE)
 			return -EINVAL;
+		spin_lock_irqsave(&pInfo->lock, flags);
 		pInfo->priority = arg & 0xff;
+		spin_unlock_irqrestore(&pInfo->lock, flags);
 		break;
 	case R3964_USE_BCC:
+		spin_lock_irqsave(&pInfo->lock, flags);
 		if (arg)
 			pInfo->flags |= R3964_BCC;
 		else
 			pInfo->flags &= ~R3964_BCC;
+		spin_unlock_irqrestore(&pInfo->lock, flags);
 		break;
 	case R3964_READ_TELEGRAM:
 		retval = read_telegram(pInfo, task_pid(current),
@@ -1256,7 +1265,6 @@ static int r3964_ioctl(struct tty_struct
 		break;
 	}
 
-	mutex_unlock(&pInfo->read_lock);
 	return retval;
 }