ANDROID: sdcardfs: Hold i_mutex for i_size_write

When we call i_size_write, we must be holding i_mutex to avoid
possible lockups on 32 bit/SMP architectures. This is not
necessary on 64 bit architectures.

Change-Id: Ic3b946507c54d81b5c9046f9b57d25d4b0f9feef
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Bug: 73287721

fs/sdcardfs/file.c

@@ -62,6 +62,7 @@ static ssize_t sdcardfs_write(struct file *file, const char __user *buf,
 	int err;
 	struct file *lower_file;
 	struct dentry *dentry = file->f_path.dentry;
+	struct inode *inode = dentry->d_inode;
 
 	/* check disk space */
 	if (!check_min_free_space(dentry, count, 0)) {
@@ -73,10 +74,12 @@ static ssize_t sdcardfs_write(struct file *file, const char __user *buf,
 	err = vfs_write(lower_file, buf, count, ppos);
 	/* update our inode times+sizes upon a successful lower write */
 	if (err >= 0) {
-		fsstack_copy_inode_size(dentry->d_inode,
-					file_inode(lower_file));
-		fsstack_copy_attr_times(dentry->d_inode,
-					file_inode(lower_file));
+		if (sizeof(loff_t) > sizeof(long))
+			mutex_lock(&inode->i_mutex);
+		fsstack_copy_inode_size(inode, file_inode(lower_file));
+		fsstack_copy_attr_times(inode, file_inode(lower_file));
+		if (sizeof(loff_t) > sizeof(long))
+			mutex_unlock(&inode->i_mutex);
 	}
 
 	return err;
@@ -391,6 +394,7 @@ ssize_t sdcardfs_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 {
 	int err;
 	struct file *file = iocb->ki_filp, *lower_file;
+	struct inode *inode = file->f_path.dentry->d_inode;
 
 	lower_file = sdcardfs_lower_file(file);
 	if (!lower_file->f_op->write_iter) {
@@ -405,10 +409,12 @@ ssize_t sdcardfs_write_iter(struct kiocb *iocb, struct iov_iter *iter)
 	fput(lower_file);
 	/* update upper inode times/sizes as needed */
 	if (err >= 0 || err == -EIOCBQUEUED) {
-		fsstack_copy_inode_size(file->f_path.dentry->d_inode,
-					file_inode(lower_file));
-		fsstack_copy_attr_times(file->f_path.dentry->d_inode,
-					file_inode(lower_file));
+		if (sizeof(loff_t) > sizeof(long))
+			mutex_lock(&inode->i_mutex);
+		fsstack_copy_inode_size(inode, file_inode(lower_file));
+		fsstack_copy_attr_times(inode, file_inode(lower_file));
+		if (sizeof(loff_t) > sizeof(long))
+			mutex_unlock(&inode->i_mutex);
 	}
 out:
 	return err;