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

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: stable <stable@vger.kernel.org>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 31 insertions, 18 deletions

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 1f6b5c8394b4..023d271c2614 100644
--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -88,7 +88,8 @@ 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;
@@ -323,7 +324,7 @@ 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);
@@ -386,7 +387,7 @@ 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;
 }
@@ -399,7 +400,7 @@ 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;
 
@@ -476,7 +477,7 @@ retry:
         rv = cntr;
 
 err:
-        mutex_unlock(&desc->lock);
+        mutex_unlock(&desc->rlock);
         return rv;
 }
 
@@ -542,7 +543,8 @@ 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;
@@ -555,7 +557,7 @@ 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);
@@ -567,9 +569,11 @@ 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");
@@ -667,7 +671,8 @@ 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;
@@ -781,10 +786,12 @@ 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);
@@ -800,8 +807,10 @@ 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 (!PMSG_IS_AUTO(message))
-                mutex_lock(&desc->lock);
+        if (!PMSG_IS_AUTO(message)) {
+                mutex_lock(&desc->rlock);
+                mutex_lock(&desc->wlock);
+        }
         spin_lock_irq(&desc->iuspin);
 
         if (PMSG_IS_AUTO(message) &&
@@ -817,8 +826,10 @@ static int wdm_suspend(struct usb_interface *intf, pm_message_t message)
                 kill_urbs(desc);
                 cancel_work_sync(&desc->rxwork);
         }
-        if (!PMSG_IS_AUTO(message))
-                mutex_unlock(&desc->lock);
+        if (!PMSG_IS_AUTO(message)) {
+                mutex_unlock(&desc->wlock);
+                mutex_unlock(&desc->rlock);
+        }
 
         return rv;
 }
@@ -856,7 +867,8 @@ 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);
 
         /*
@@ -878,7 +890,8 @@ 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;
 }