Revert "functionfs: fix the open/removal races"

This reverts commit b49c766 which is
commit e5bf5ee upstream.

It has been reported to cause test problems in Android devices.  As the
other functionfs changes were not also backported at the same time,
something is out of sync.  So just revert this one for now and it can
come back in the future as a patch series if it is tested.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gregkh

drivers/usb/gadget/function/f_fs.c

@@ -640,22 +640,13 @@ static ssize_t ffs_ep0_read(struct file *file, char __user *buf,
 
 static int ffs_ep0_open(struct inode *inode, struct file *file)
 {
-	struct ffs_data *ffs = inode->i_sb->s_fs_info;
-	int ret;
+	struct ffs_data *ffs = inode->i_private;
 
-	/* Acquire mutex */
-	ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
-	if (ret < 0)
-		return ret;
-
-	ffs_data_opened(ffs);
-	if (ffs->state == FFS_CLOSING) {
-		ffs_data_closed(ffs);
-		mutex_unlock(&ffs->mutex);
+	if (ffs->state == FFS_CLOSING)
 		return -EBUSY;
-	}
-	mutex_unlock(&ffs->mutex);
+
 	file->private_data = ffs;
+	ffs_data_opened(ffs);
 
 	return stream_open(inode, file);
 }
@@ -1202,33 +1193,14 @@ static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
 static int
 ffs_epfile_open(struct inode *inode, struct file *file)
 {
-	struct ffs_data *ffs = inode->i_sb->s_fs_info;
-	struct ffs_epfile *epfile;
-	int ret;
+	struct ffs_epfile *epfile = inode->i_private;
 
-	/* Acquire mutex */
-	ret = ffs_mutex_lock(&ffs->mutex, file->f_flags & O_NONBLOCK);
-	if (ret < 0)
-		return ret;
-
-	if (!atomic_inc_not_zero(&ffs->opened)) {
-		mutex_unlock(&ffs->mutex);
-		return -ENODEV;
-	}
-	/*
-	 * we want the state to be FFS_ACTIVE; FFS_ACTIVE alone is
-	 * not enough, though - we might have been through FFS_CLOSING
-	 * and back to FFS_ACTIVE, with our file already removed.
-	 */
-	epfile = smp_load_acquire(&inode->i_private);
-	if (unlikely(ffs->state != FFS_ACTIVE || !epfile)) {
-		mutex_unlock(&ffs->mutex);
-		ffs_data_closed(ffs);
+	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
 		return -ENODEV;
-	}
-	mutex_unlock(&ffs->mutex);
 
 	file->private_data = epfile;
+	ffs_data_opened(epfile->ffs);
+
 	return stream_open(inode, file);
 }
 
@@ -1360,7 +1332,7 @@ static void ffs_dmabuf_put(struct dma_buf_attachment *attach)
 static int
 ffs_epfile_release(struct inode *inode, struct file *file)
 {
-	struct ffs_epfile *epfile = file->private_data;
+	struct ffs_epfile *epfile = inode->i_private;
 	struct ffs_dmabuf_priv *priv, *tmp;
 	struct ffs_data *ffs = epfile->ffs;
 
@@ -2380,19 +2352,14 @@ static int ffs_epfiles_create(struct ffs_data *ffs)
 	return 0;
 }
 
-static void clear_one(struct dentry *dentry)
-{
-	smp_store_release(&dentry->d_inode->i_private, NULL);
-}
-
 static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
 {
 	struct ffs_epfile *epfile = epfiles;
 
 	for (; count; --count, ++epfile) {
 		BUG_ON(mutex_is_locked(&epfile->mutex));
 		if (epfile->dentry) {
-			simple_recursive_removal(epfile->dentry, clear_one);
+			simple_recursive_removal(epfile->dentry, NULL);
 			epfile->dentry = NULL;
 		}
 	}