fix page release issue in filemap_fault

find_lock_page increases page's usage count, we should decrease it
before return VM_FAULT_SIGBUS

Signed-off-by: Yan Zheng<yanzheng@21cn.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -1388,6 +1388,7 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	size = (i_size_read(inode) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
 	if (unlikely(vmf->pgoff >= size)) {
 		unlock_page(page);
+		page_cache_release(page);
 		goto outside_data_content;
 	}