lib: kunit_iov_iter: fix memory leaks

Use vfree() instead of vunmap() to free the buffer allocated by
iov_kunit_create_buffer() because vunmap() does not honour
VM_MAP_PUT_PAGES.  In order for this to work the page array itself must
not be managed by kunit.

Remove the folio_put() when destroying a folioq.  This is handled by
vfree(), now.

Pointed out by sashiko.dev on a previous iteration of this series.

Tested by running the kunit test 10000 times in a loop.

Link: https://lkml.kernel.org/r/20260326214905.818170-4-lk@c--e.de
Fixes: 2d71340 ("iov_iter: Kunit tests for copying to/from an iterator")
Signed-off-by: Christian A. Ehrhardt <lk@c--e.de>
Cc: David Howells <dhowells@redhat.com>
Cc: David Gow <davidgow@google.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: Christian A. Ehrhardt

lib/tests/kunit_iov_iter.c

@@ -42,7 +42,7 @@ static inline u8 pattern(unsigned long x)
 
 static void iov_kunit_unmap(void *data)
 {
-	vunmap(data);
+	vfree(data);
 }
 
 static void *__init iov_kunit_create_buffer(struct kunit *test,
@@ -53,17 +53,22 @@ static void *__init iov_kunit_create_buffer(struct kunit *test,
 	unsigned long got;
 	void *buffer;
 
-	pages = kunit_kcalloc(test, npages, sizeof(struct page *), GFP_KERNEL);
-        KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pages);
+	pages = kzalloc_objs(struct page *, npages, GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, pages);
 	*ppages = pages;
 
 	got = alloc_pages_bulk(GFP_KERNEL, npages, pages);
 	if (got != npages) {
 		release_pages(pages, got);
+		kvfree(pages);
 		KUNIT_ASSERT_EQ(test, got, npages);
 	}
 
 	buffer = vmap(pages, npages, VM_MAP | VM_MAP_PUT_PAGES, PAGE_KERNEL);
+	if (buffer == NULL) {
+		release_pages(pages, got);
+		kvfree(pages);
+	}
         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, buffer);
 
 	kunit_add_action_or_reset(test, iov_kunit_unmap, buffer);
@@ -369,9 +374,6 @@ static void iov_kunit_destroy_folioq(void *data)
 
 	for (folioq = data; folioq; folioq = next) {
 		next = folioq->next;
-		for (int i = 0; i < folioq_nr_slots(folioq); i++)
-			if (folioq_folio(folioq, i))
-				folio_put(folioq_folio(folioq, i));
 		kfree(folioq);
 	}
 }