1 files changed, 38 insertions, 17 deletions

diff --git a/fs/sdcardfs/mmap.c b/fs/sdcardfs/mmap.c
index e21f64675a80..0d4089c62c3a 100644
--- a/fs/sdcardfs/mmap.c
+++ b/fs/sdcardfs/mmap.c
@@ -48,34 +48,55 @@ static int sdcardfs_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	return err;
 }
 
+static int sdcardfs_page_mkwrite(struct vm_area_struct *vma,
+			       struct vm_fault *vmf)
+{
+	int err = 0;
+	struct file *file, *lower_file;
+	const struct vm_operations_struct *lower_vm_ops;
+	struct vm_area_struct lower_vma;
+
+	memcpy(&lower_vma, vma, sizeof(struct vm_area_struct));
+	file = lower_vma.vm_file;
+	lower_vm_ops = SDCARDFS_F(file)->lower_vm_ops;
+	BUG_ON(!lower_vm_ops);
+	if (!lower_vm_ops->page_mkwrite)
+		goto out;
+
+	lower_file = sdcardfs_lower_file(file);
+	/*
+	 * XXX: vm_ops->page_mkwrite may be called in parallel.
+	 * Because we have to resort to temporarily changing the
+	 * vma->vm_file to point to the lower file, a concurrent
+	 * invocation of sdcardfs_page_mkwrite could see a different
+	 * value.  In this workaround, we keep a different copy of the
+	 * vma structure in our stack, so we never expose a different
+	 * value of the vma->vm_file called to us, even temporarily.
+	 * A better fix would be to change the calling semantics of
+	 * ->page_mkwrite to take an explicit file pointer.
+	 */
+	lower_vma.vm_file = lower_file;
+	err = lower_vm_ops->page_mkwrite(&lower_vma, vmf);
+out:
+	return err;
+}
+
 static ssize_t sdcardfs_direct_IO(struct kiocb *iocb,
 		struct iov_iter *iter, loff_t pos)
 {
 	/*
-     * This function returns zero on purpose in order to support direct IO.
-	 * __dentry_open checks a_ops->direct_IO and returns EINVAL if it is null.
-     *
-	 * However, this function won't be called by certain file operations
-     * including generic fs functions.  * reads and writes are delivered to
-     * the lower file systems and the direct IOs will be handled by them.
-	 *
-     * NOTE: exceptionally, on the recent kernels (since Linux 3.8.x),
-     * swap_writepage invokes this function directly.
+	 * This function should never be called directly.  We need it
+	 * to exist, to get past a check in open_check_o_direct(),
+	 * which is called from do_last().
 	 */
-	printk(KERN_INFO "%s, operation is not supported\n", __func__);
-	return 0;
+	return -EINVAL;
 }
 
-/*
- * XXX: the default address_space_ops for sdcardfs is empty.  We cannot set
- * our inode->i_mapping->a_ops to NULL because too many code paths expect
- * the a_ops vector to be non-NULL.
- */
 const struct address_space_operations sdcardfs_aops = {
-	/* empty on purpose */
 	.direct_IO	= sdcardfs_direct_IO,
 };
 
 const struct vm_operations_struct sdcardfs_vm_ops = {
 	.fault		= sdcardfs_fault,
+	.page_mkwrite	= sdcardfs_page_mkwrite,
 };