diff --git a/fs/open.c b/fs/open.c
index e53af13..f76e960 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -852,8 +852,17 @@ static int do_dentry_open(struct file *f,
 	 * XXX: Huge page cache doesn't support writing yet. Drop all page
 	 * cache for this file before processing writes.
 	 */
-	if ((f->f_mode & FMODE_WRITE) && filemap_nr_thps(inode->i_mapping))
-		truncate_pagecache(inode, 0);
+	if (f->f_mode & FMODE_WRITE) {
+		/*
+		 * Paired with smp_mb() in collapse_file() to ensure nr_thps
+		 * is up to date and the update to i_writecount by
+		 * get_write_access() is visible. Ensures subsequent insertion
+		 * of THPs into the page cache will fail.
+		 */
+		smp_mb();
+		if (filemap_nr_thps(inode->i_mapping))
+			truncate_pagecache(inode, 0);
+	}
 
 	return 0;
 
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d97b20f..b0412be 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -457,7 +457,8 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
 
 	/* Read-only file mappings need to be aligned for THP to work. */
 	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
-	    (vm_flags & VM_DENYWRITE)) {
+	    !inode_is_open_for_write(vma->vm_file->f_inode) &&
+	    (vm_flags & VM_EXEC)) {
 		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
 				HPAGE_PMD_NR);
 	}
@@ -1862,6 +1863,19 @@ static void collapse_file(struct mm_struct *mm,
 	else {
 		__mod_lruvec_page_state(new_page, NR_FILE_THPS, nr);
 		filemap_nr_thps_inc(mapping);
+		/*
+		 * Paired with smp_mb() in do_dentry_open() to ensure
+		 * i_writecount is up to date and the update to nr_thps is
+		 * visible. Ensures the page cache will be truncated if the
+		 * file is opened writable.
+		 */
+		smp_mb();
+		if (inode_is_open_for_write(mapping->host)) {
+			result = SCAN_FAIL;
+			__mod_lruvec_page_state(new_page, NR_FILE_THPS, -nr);
+			filemap_nr_thps_dec(mapping);
+			goto xa_locked;
+		}
 	}
 
 	if (nr_none) {