[PATCH 2/7] fs: Switch to page_mkwrite_check_truncate in block_page_mkwrite

[Andreas Gruenbacher <agruenba@redhat.com>]

Use the "page has been truncated" logic in page_mkwrite_check_truncate
instead of reimplementing it here.  Other than with the existing code,
fail with -EFAULT / VM_FAULT_NOPAGE when page_offset(page) == size here
as well, as should be expected.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/buffer.c | 16 +++-------------
 1 file changed, 3 insertions(+), 13 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index b8d28370cfd7..31a9a02878a2 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2499,23 +2499,13 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 	struct page *page = vmf->page;
 	struct inode *inode = file_inode(vma->vm_file);
 	unsigned long end;
-	loff_t size;
 	int ret;
 
 	lock_page(page);
-	size = i_size_read(inode);
-	if ((page->mapping != inode->i_mapping) ||
-	    (page_offset(page) > size)) {
-		/* We overload EFAULT to mean page got truncated */
-		ret = -EFAULT;
+	ret = page_mkwrite_check_truncate(page, inode);
+	if (ret < 0)
 		goto out_unlock;
-	}
-
-	/* page is wholly or partially inside EOF */
-	if (((page->index + 1) << PAGE_SHIFT) > size)
-		end = size & ~PAGE_MASK;
-	else
-		end = PAGE_SIZE;
+	end = ret;
 
 	ret = __block_write_begin(page, 0, end, get_block);
 	if (!ret)
-- 
2.24.1