mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page

If a new hugetlb page is allocated during fallocate it will not be
marked as active (set_page_huge_active) which will result in a later
isolate_huge_page failure when the page migration code would like to
move that page.  Such a failure would be unexpected and wrong.

Only export set_page_huge_active, just leave clear_page_huge_active as
static.  Because there are no external users.

Link: https://lkml.kernel.org/r/20210115124942.46403-3-songmuchun@bytedance.com
Fixes: 70c3547e (hugetlbfs: add hugetlbfs_fallocate())
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hugetlbfs/inode.c

@@ -735,9 +735,10 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 
 		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 
+		set_page_huge_active(page);
 		/*
 		 * unlock_page because locked by add_to_page_cache()
-		 * page_put due to reference from alloc_huge_page()
+		 * put_page() due to reference from alloc_huge_page()
 		 */
 		unlock_page(page);
 		put_page(page);

include/linux/hugetlb.h

@@ -770,6 +770,8 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 }
 #endif
 
+void set_page_huge_active(struct page *page);
+
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 

mm/hugetlb.c

@@ -1349,7 +1349,7 @@ bool page_huge_active(struct page *page)
 }
 
 /* never called for tail page */
-static void set_page_huge_active(struct page *page)
+void set_page_huge_active(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
 	SetPagePrivate(&page[1]);