cuse: use mutex as registration lock instead of spinlocks

We need to check for name-collisions during cuse-device registration. To
avoid race-conditions, this needs to be protected during the whole device
registration. Therefore, replace the spinlocks by mutexes first so we can
safely extend the locked regions to include more expensive or sleeping
code paths.
Signed-off-by: NDavid Herrmann <dh.herrmann@googlemail.com>
Acked-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

fs/fuse/cuse.c

@@ -45,7 +45,6 @@
 #include <linux/miscdevice.h>
 #include <linux/mutex.h>
 #include <linux/slab.h>
-#include <linux/spinlock.h>
 #include <linux/stat.h>
 #include <linux/module.h>
 
@@ -63,7 +62,7 @@ struct cuse_conn {
 	bool			unrestricted_ioctl;
 };
 
-static DEFINE_SPINLOCK(cuse_lock);		/* protects cuse_conntbl */
+static DEFINE_MUTEX(cuse_lock);		/* protects registration */
 static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN];
 static struct class *cuse_class;
 
@@ -114,14 +113,14 @@ static int cuse_open(struct inode *inode, struct file *file)
 	int rc;
 
 	/* look up and get the connection */
-	spin_lock(&cuse_lock);
+	mutex_lock(&cuse_lock);
 	list_for_each_entry(pos, cuse_conntbl_head(devt), list)
 		if (pos->dev->devt == devt) {
 			fuse_conn_get(&pos->fc);
 			cc = pos;
 			break;
 		}
-	spin_unlock(&cuse_lock);
+	mutex_unlock(&cuse_lock);
 
 	/* dead? */
 	if (!cc)
@@ -377,9 +376,9 @@ static void cuse_process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
 	cc->cdev = cdev;
 
 	/* make the device available */
-	spin_lock(&cuse_lock);
+	mutex_lock(&cuse_lock);
 	list_add(&cc->list, cuse_conntbl_head(devt));
-	spin_unlock(&cuse_lock);
+	mutex_unlock(&cuse_lock);
 
 	/* announce device availability */
 	dev_set_uevent_suppress(dev, 0);
@@ -520,9 +519,9 @@ static int cuse_channel_release(struct inode *inode, struct file *file)
 	int rc;
 
 	/* remove from the conntbl, no more access from this point on */
-	spin_lock(&cuse_lock);
+	mutex_lock(&cuse_lock);
 	list_del_init(&cc->list);
-	spin_unlock(&cuse_lock);
+	mutex_unlock(&cuse_lock);
 
 	/* remove device */
 	if (cc->dev)