Commit 49a4e7186b08 ("selftests/mm: thuge-gen: add setup of HugeTLB pages")
changed thuge-gen test to use common functions for reading hugetlb
attributes from sysfs, but it missed that the original read_free() function
special cased PAGE_SIZE tests.

For PAGE_SIZE tests, failure to read sysfs was ignored and read_free()
returned 0.

This allowed test_shmget() to essentially skip the check of how many huge
pages was consumed when it ran with PAGE_SIZE.

Commit 3199b0c09efa ("selftests/mm: fix read_file() return value check")
fixed checks for read_file() return value and this exposed the issue in
test_shmget() that checks the number of free hugetlb pages even for
PAGE_SIZE test, tries to access

/sys/kernel/mm/hugepages/hugepages-<PAGE_SIZE>/free_hugepages

and obviously fails there.

Gate the checks for free huge pages on size != getpagesize() and initialize
before and after variables to values matching PAGE_SIZE test.

Fixes: 49a4e7186b08 ("selftests/mm: thuge-gen: add setup of HugeTLB pages")
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Sarthak Sharma <sarthak.sharma@arm.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
v2 changes:
* Correct the commit message

v1: https://patch.msgid.link/20260809-selftests-thuge-gen-fix-v1-1-1919f4b3d12f@kernel.org
---
 tools/testing/selftests/mm/thuge-gen.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/mm/thuge-gen.c b/tools/testing/selftests/mm/thuge-gen.c
index 22b9c2f1c35d..50d0805b65db 100644
--- a/tools/testing/selftests/mm/thuge-gen.c
+++ b/tools/testing/selftests/mm/thuge-gen.c
@@ -71,12 +71,16 @@ void test_mmap(unsigned long size, unsigned flags)
 
 void test_shmget(unsigned long size, unsigned flags)
 {
-	int id;
-	unsigned long before, after;
+	/* values for PAGE_SIZE test */
+	unsigned long before = NUM_PAGES;
+	unsigned long after = 0;
 	struct shm_info i;
 	char *map;
+	int id;
+
+	if (size != getpagesize())
+		before = hugetlb_free_pages(size);
 
-	before = hugetlb_free_pages(size);
 	id = shmget(IPC_PRIVATE, size * NUM_PAGES, IPC_CREAT|0600|flags);
 	if (id < 0) {
 		if (errno == EPERM) {
@@ -97,10 +101,11 @@ void test_shmget(unsigned long size, unsigned flags)
 	shmctl(id, IPC_RMID, NULL);
 
 	memset(map, 0xff, size*NUM_PAGES);
-	after = hugetlb_free_pages(size);
+	if (size != getpagesize())
+		after = hugetlb_free_pages(size);
 
 	show(size);
-	ksft_test_result(size == getpagesize() || (before - after) == NUM_PAGES,
+	ksft_test_result((before - after) == NUM_PAGES,
 			 "%s: mmap %lu %x\n", __func__, size, flags);
 	if (shmdt(map))
 		ksft_exit_fail_msg("%s: shmdt: %s\n", __func__, strerror(errno));

---
base-commit: 17e5919bdca144d4e67337f53bf57d7811f62192
change-id: 20260809-selftests-thuge-gen-fix-5ac05f56307c

--
Sincerely yours,
Mike.