ODROID-C2: gpu/ump: fix crash error caused by 'mmap()'

This patch is contributed by 'scpcom' in Hardkernel's forum.
 * http://seafile.servator.de/sbc/odroid/build/linux-3.16.y-amlogic-gpu_arm_fix_mmap_permissions.patch

Change-Id: I250e6a8fe96895135a39babf156aaff702c61606
Signed-off-by: Dongjin Kim <[email protected]>

Author: tobetter

drivers/gpu/arm/ump/linux/ump_kernel_linux.c

@@ -512,6 +512,17 @@ static int ump_file_mmap(struct file *filp, struct vm_area_struct *vma)
 	/* By setting this flag, during a process fork; the child process will not have the parent UMP mappings */
 	vma->vm_flags |= VM_DONTCOPY;
 
+	/* Test if we can make the mapping writable */
+	if (mapping_map_writable(filp->f_mapping)) {
+		/* On error, we need to allow it for forced VM_SHARED */
+		mapping_allow_writable(filp->f_mapping);
+		DBG_MSG(3, ("UMP Map function: Forcing allow writable\n"));
+	}
+	else {
+		/* On success, the counter got incremented, decrement the counter */
+		mapping_unmap_writable(filp->f_mapping);
+	}
+
 	DBG_MSG(4, ("UMP vma->flags: %x\n", vma->vm_flags));
 
 	/* Call the common mmap handler */