hostfs: hostfs_file_open: Switch to data locking model

Instead of serializing hostfs_file_open() we can use
a per inode mutex to protect ->mode.
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/hostfs/hostfs_kern.c

@@ -24,6 +24,7 @@ struct hostfs_inode_info {
 	int fd;
 	fmode_t mode;
 	struct inode vfs_inode;
+	struct mutex open_mutex;
 };
 
 static inline struct hostfs_inode_info *HOSTFS_I(struct inode *inode)
@@ -225,6 +226,7 @@ static struct inode *hostfs_alloc_inode(struct super_block *sb)
 	hi->fd = -1;
 	hi->mode = 0;
 	inode_init_once(&hi->vfs_inode);
+	mutex_init(&hi->open_mutex);
 	return &hi->vfs_inode;
 }
 
@@ -295,7 +297,6 @@ static int hostfs_readdir(struct file *file, struct dir_context *ctx)
 
 static int hostfs_file_open(struct inode *ino, struct file *file)
 {
-	static DEFINE_MUTEX(open_mutex);
 	char *name;
 	fmode_t mode = 0;
 	int err;
@@ -324,15 +325,15 @@ static int hostfs_file_open(struct inode *ino, struct file *file)
 	if (fd < 0)
 		return fd;
 
-	mutex_lock(&open_mutex);
+	mutex_lock(&HOSTFS_I(ino)->open_mutex);
 	/* somebody else had handled it first? */
 	if ((mode & HOSTFS_I(ino)->mode) == mode) {
-		mutex_unlock(&open_mutex);
+		mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 		return 0;
 	}
 	if ((mode | HOSTFS_I(ino)->mode) != mode) {
 		mode |= HOSTFS_I(ino)->mode;
-		mutex_unlock(&open_mutex);
+		mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 		close_file(&fd);
 		goto retry;
 	}
@@ -342,12 +343,12 @@ static int hostfs_file_open(struct inode *ino, struct file *file)
 		err = replace_file(fd, HOSTFS_I(ino)->fd);
 		close_file(&fd);
 		if (err < 0) {
-			mutex_unlock(&open_mutex);
+			mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 			return err;
 		}
 	}
 	HOSTFS_I(ino)->mode = mode;
-	mutex_unlock(&open_mutex);
+	mutex_unlock(&HOSTFS_I(ino)->open_mutex);
 
 	return 0;
 }