9p: don't bother with private lock in ->d_fsdata; dentry->d_lock will do just fine

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/9p/fid.c

@@ -54,14 +54,13 @@ int v9fs_fid_add(struct dentry *dentry, struct p9_fid *fid)
 		if (!dent)
 			return -ENOMEM;
 
-		spin_lock_init(&dent->lock);
 		INIT_LIST_HEAD(&dent->fidlist);
 		dentry->d_fsdata = dent;
 	}
 
-	spin_lock(&dent->lock);
+	spin_lock(&dentry->d_lock);
 	list_add(&fid->dlist, &dent->fidlist);
-	spin_unlock(&dent->lock);
+	spin_unlock(&dentry->d_lock);
 
 	return 0;
 }
@@ -85,14 +84,14 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
 	dent = (struct v9fs_dentry *) dentry->d_fsdata;
 	ret = NULL;
 	if (dent) {
-		spin_lock(&dent->lock);
+		spin_lock(&dentry->d_lock);
 		list_for_each_entry(fid, &dent->fidlist, dlist) {
 			if (any || uid_eq(fid->uid, uid)) {
 				ret = fid;
 				break;
 			}
 		}
-		spin_unlock(&dent->lock);
+		spin_unlock(&dentry->d_lock);
 	}
 
 	return ret;

fs/9p/fid.h

@@ -25,7 +25,6 @@
 
 /**
  * struct v9fs_dentry - 9p private data stored in dentry d_fsdata
- * @lock: protects the fidlist
  * @fidlist: list of FIDs currently associated with this dentry
  *
  * This structure defines the 9p private data associated with
@@ -35,11 +34,12 @@
  * inodes in order to more closely map functionality to the Plan 9
  * expected behavior for FID reclaimation and tracking.
  *
+ * Protected by ->d_lock of dentry it belongs to.
+ *
  * See Also: Mapping FIDs to Linux VFS model in
  * Design and Implementation of the Linux 9P File System documentation
  */
 struct v9fs_dentry {
-	spinlock_t lock; /* protect fidlist */
 	struct list_head fidlist;
 };