USB: cdc-wdm: use two mutexes to allow simultaneous read and write

commit e8537bd2c4f325a4796da33564ddcef9489b7feb upstream.

using a separate read and write mutex for locking is sufficient to make the
driver accept simultaneous read and write. This improves useability a lot.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Varun Wadekar <vwadekar@nvidia.com>
Change-Id: I10ed5f0e41b379f0fef8a22abde46d4231162ff9
Reviewed-on: http://git-master/r/79672
Reviewed-by: Simone Willett <swillett@nvidia.com>
Tested-by: Simone Willett <swillett@nvidia.com>

1 files changed, 31 insertions, 18 deletions

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index f5eb38d03e69..b1472c31ab75 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -90,7 +90,8 @@ struct wdm_device {
 	int			count;
 	dma_addr_t		shandle;
 	dma_addr_t		ihandle;
-	struct mutex		lock;
+	struct mutex		wlock;
+	struct mutex		rlock;
 	wait_queue_head_t	wait;
 	struct work_struct	rxwork;
 	int			werr;
@@ -325,7 +326,7 @@ static ssize_t wdm_write
 	}
 
 	/* concurrent writes and disconnect */
-	r = mutex_lock_interruptible(&desc->lock);
+	r = mutex_lock_interruptible(&desc->wlock);
 	rv = -ERESTARTSYS;
 	if (r) {
 		kfree(buf);
@@ -388,7 +389,7 @@ static ssize_t wdm_write
 out:
 	usb_autopm_put_interface(desc->intf);
 outnp:
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->wlock);
 outnl:
 	return rv < 0 ? rv : count;
 }
@@ -401,7 +402,7 @@ static ssize_t wdm_read
 	struct wdm_device *desc = file->private_data;
 
 
-	rv = mutex_lock_interruptible(&desc->lock); /*concurrent reads */
+	rv = mutex_lock_interruptible(&desc->rlock); /*concurrent reads */
 	if (rv < 0)
 		return -ERESTARTSYS;
 
@@ -478,7 +479,7 @@ retry:
 	rv = cntr;
 
 err:
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->rlock);
 	return rv;
 }
 
@@ -544,7 +545,8 @@ static int wdm_open(struct inode *inode, struct file *file)
 	}
 	intf->needs_remote_wakeup = 1;
 
-	mutex_lock(&desc->lock);
+	/* using write lock to protect desc->count */
+	mutex_lock(&desc->wlock);
 	if (!desc->count++) {
 		desc->werr = 0;
 		desc->rerr = 0;
@@ -557,7 +559,7 @@ static int wdm_open(struct inode *inode, struct file *file)
 	} else {
 		rv = 0;
 	}
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->wlock);
 	usb_autopm_put_interface(desc->intf);
 out:
 	mutex_unlock(&wdm_mutex);
@@ -569,9 +571,11 @@ static int wdm_release(struct inode *inode, struct file *file)
 	struct wdm_device *desc = file->private_data;
 
 	mutex_lock(&wdm_mutex);
-	mutex_lock(&desc->lock);
+
+	/* using write lock to protect desc->count */
+	mutex_lock(&desc->wlock);
 	desc->count--;
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->wlock);
 
 	if (!desc->count) {
 		dev_dbg(&desc->intf->dev, "wdm_release: cleanup");
@@ -669,7 +673,8 @@ next_desc:
 	desc = kzalloc(sizeof(struct wdm_device), GFP_KERNEL);
 	if (!desc)
 		goto out;
-	mutex_init(&desc->lock);
+	mutex_init(&desc->rlock);
+	mutex_init(&desc->wlock);
 	spin_lock_init(&desc->iuspin);
 	init_waitqueue_head(&desc->wait);
 	desc->wMaxCommand = maxcom;
@@ -783,10 +788,12 @@ static void wdm_disconnect(struct usb_interface *intf)
 	/* to terminate pending flushes */
 	clear_bit(WDM_IN_USE, &desc->flags);
 	spin_unlock_irqrestore(&desc->iuspin, flags);
-	mutex_lock(&desc->lock);
+	mutex_lock(&desc->rlock);
+	mutex_lock(&desc->wlock);
 	kill_urbs(desc);
 	cancel_work_sync(&desc->rxwork);
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->wlock);
+	mutex_unlock(&desc->rlock);
 	wake_up_all(&desc->wait);
 	if (!desc->count)
 		cleanup(desc);
@@ -802,8 +809,10 @@ static int wdm_suspend(struct usb_interface *intf, pm_message_t message)
 	dev_dbg(&desc->intf->dev, "wdm%d_suspend\n", intf->minor);
 
 	/* if this is an autosuspend the caller does the locking */
-	if (!(message.event & PM_EVENT_AUTO))
-		mutex_lock(&desc->lock);
+	if (!(message.event & PM_EVENT_AUTO)) {
+		mutex_lock(&desc->rlock);
+		mutex_lock(&desc->wlock);
+	}
 	spin_lock_irq(&desc->iuspin);
 
 	if ((message.event & PM_EVENT_AUTO) &&
@@ -819,8 +828,10 @@ static int wdm_suspend(struct usb_interface *intf, pm_message_t message)
 		kill_urbs(desc);
 		cancel_work_sync(&desc->rxwork);
 	}
-	if (!(message.event & PM_EVENT_AUTO))
-		mutex_unlock(&desc->lock);
+	if (!(message.event & PM_EVENT_AUTO)) {
+		mutex_unlock(&desc->wlock);
+		mutex_unlock(&desc->rlock);
+	}
 
 	return rv;
 }
@@ -858,7 +869,8 @@ static int wdm_pre_reset(struct usb_interface *intf)
 {
 	struct wdm_device *desc = usb_get_intfdata(intf);
 
-	mutex_lock(&desc->lock);
+	mutex_lock(&desc->rlock);
+	mutex_lock(&desc->wlock);
 	kill_urbs(desc);
 
 	/*
@@ -880,7 +892,8 @@ static int wdm_post_reset(struct usb_interface *intf)
 	int rv;
 
 	rv = recover_from_urb_loss(desc);
-	mutex_unlock(&desc->lock);
+	mutex_unlock(&desc->wlock);
+	mutex_unlock(&desc->rlock);
 	return 0;
 }