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>

diff --git a/drivers/usb/class/cdc-wdm.c b/drivers/usb/class/cdc-wdm.c
index 1f6b5c8394b4a9116d7aeb9935fee7683bdea251..023d271c2614e674177db6b4063736cddc23d9a3 100644 (file)
--- 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;
 }