[PATCH v2 1/3] selftests/mm: compaction_test: Fix bogus test success on Aarch64

[Dev Jain]

Currently, if at runtime we are not able to allocate a huge page, the
test will trivially pass on Aarch64 due to no exception being raised on
division by zero while computing compaction_index. Fix that by checking
for nr_hugepages == 0. Anyways, in general, avoid a division by zero by
exiting the program beforehand. While at it, fix a typo, and handle the
case where the number of hugepages may overflow an integer.

Changes in v2:
- Combine with this series, handle unsigned long number of hugepages

v1:
- https://lore.kernel.org/all/20240513082842.4117782-1-dev.jain@xxxxxxx/

Fixes: bd67d5c15cc1 ("Test compaction of mlocked memory")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Dev Jain <dev.jain@xxxxxxx>
---
 tools/testing/selftests/mm/compaction_test.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/mm/compaction_test.c b/tools/testing/selftests/mm/compaction_test.c
index 4f42eb7d7636..0b249a06a60b 100644
--- a/tools/testing/selftests/mm/compaction_test.c
+++ b/tools/testing/selftests/mm/compaction_test.c
@@ -82,12 +82,13 @@ int prereq(void)
 	return -1;
 }
 
-int check_compaction(unsigned long mem_free, unsigned int hugepage_size)
+int check_compaction(unsigned long mem_free, unsigned long hugepage_size)
 {
+	unsigned long nr_hugepages_ul;
 	int fd, ret = -1;
 	int compaction_index = 0;
-	char initial_nr_hugepages[10] = {0};
-	char nr_hugepages[10] = {0};
+	char initial_nr_hugepages[20] = {0};
+	char nr_hugepages[20] = {0};
 
 	/* We want to test with 80% of available memory. Else, OOM killer comes
 	   in to play */
@@ -134,7 +135,12 @@ int check_compaction(unsigned long mem_free, unsigned int hugepage_size)
 
 	/* We should have been able to request at least 1/3 rd of the memory in
 	   huge pages */
-	compaction_index = mem_free/(atoi(nr_hugepages) * hugepage_size);
+	nr_hugepages_ul = strtoul(nr_hugepages, NULL, 10);
+	if (!nr_hugepages_ul) {
+		ksft_print_msg("ERROR: No memory is available as huge pages\n");
+		goto close_fd;
+	}
+	compaction_index = mem_free/(nr_hugepages_ul * hugepage_size);
 
 	lseek(fd, 0, SEEK_SET);
 
@@ -145,11 +151,11 @@ int check_compaction(unsigned long mem_free, unsigned int hugepage_size)
 		goto close_fd;
 	}
 
-	ksft_print_msg("Number of huge pages allocated = %d\n",
-		       atoi(nr_hugepages));
+	ksft_print_msg("Number of huge pages allocated = %lu\n",
+		       nr_hugepages_ul);
 
 	if (compaction_index > 3) {
-		ksft_print_msg("ERROR: Less that 1/%d of memory is available\n"
+		ksft_print_msg("ERROR: Less than 1/%d of memory is available\n"
 			       "as huge pages\n", compaction_index);
 		goto close_fd;
 	}
-- 
2.34.1