selftests/mm: avoid false failures in hugetlb and KSM tests

Hi all,

This series fixes issues in the hugetlb and KSM MM selftest categories that can report failures when the prerequisites for the tests are not satisfied.

Patch 1 updates the hugetlb selftest helpers to handle -EINVAL when attempting to configure gigantic HugeTLB pages via nr_hugepages. PowerPC hash MMU pSeries systems expose gigantic hugepage sizes but do not allow runtime allocation of such pages, causing the sysfs write to fail. Handle this case gracefully and continue running the test instead of aborting.

Patch 2 fixes the KSM NUMA merge test on systems with memoryless NUMA nodes. The test currently relies on the number of configured NUMA nodes and may attempt allocations on nodes that have no memory, resulting in spurious failures. Use the existing helpers to identify
NUMA nodes that contain memory and skip the test when fewer than two such nodes are available.

Patch 3 fixes a pre-existing operator precedence issue in ksm_tests, where a ternary expression combined with logical OR operators could be evaluated differently than intended. Added parentheses to ensure the correct evaluation order.

These changes improve handling of unsupported test configurations and unmet test prerequisites, avoiding spurious failures.

Thanks,
Sayali
---

V2 -> V3:
- For "selftests/mm: handle EINVAL when configuring gigantic hugepages":
Reworked the implementation to use internal helper functions with an ignore_einval flag, as suggested by David Hildenbrand.
Added __write_file() and __write_num() helpers to optionally ignore -EINVAL from sysfs writes.
Added write_num_ignore_einval() wrapper for callers that need to tolerate unsupported hugepage configurations.

V2: https://lore.kernel.org/all/[email protected]/

---

V1 -> V2:
- For "selftests/mm: handle EINVAL when configuring gigantic hugepages":
Added a dedicated hugetlb_write_num() helper to handle the expected EINVAL returned by gigantic hugepage configuration, in the
hugepage setup code rather than modifying the generic write_file() helper.
- For "selftests/mm: fix ksm NUMA merge test for systems with memoryless NUMA nodes":
Updated implementation as per David's review comment to build upon existing helpers get_next_mem_node().
- Added new patch "selftests/mm: fix ternary operator precedence in ksm_tests" to address a pre-existing issue identified during Sahiko's review.

V1: https://lore.kernel.org/all/[email protected]/

---

Sayali Patil (3):
selftests/mm: handle EINVAL when configuring gigantic hugepages selftests/mm: fix ksm NUMA merge test for systems with memoryless NUMA
nodes
selftests/mm: fix ternary operator precedence in ksm_tests

 .../testing/selftests/mm/hugepage_settings.c  |  2 +-
 tools/testing/selftests/mm/ksm_tests.c        | 28 ++++++++++---------
 tools/testing/selftests/mm/vm_util.c          | 26 ++++++++++++++---
 tools/testing/selftests/mm/vm_util.h          |  1 +
 4 files changed, 39 insertions(+), 18 deletions(-)

2.52.0

The KSM NUMA merge test allocates identical pages on different NUMA nodes and verifies KSM behavior with merge_across_nodes enabled and disabled.

On systems with memoryless NUMA nodes, for example:
#numactl -H

      available: 2 nodes (0,4)
      .....
      node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
      node 0 size: 14825 MB
      node 0 free: 1382 MB
      node 4 cpus:
      node 4 size: 0 MB
      node 4 free: 0 MB

the test may attempt to allocate memory on a node without memory, causing numa_alloc_onnode() to fail and resulting in a spurious test failure.

The test currently checks numa_num_configured_nodes() to determine whether sufficient NUMA nodes are available. However, configured nodes do not necessarily have memory.

Reuse the existing get_first_mem_node() and get_next_mem_node() helpers to locate NUMA nodes that actually contain memory, and skip the test when fewer than two such nodes are available.

Before patch:
---------------------------
running ./ksm_tests -N -m 1
---------------------------
mbind: Invalid argument
ok 1 KSM NUMA merging
Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 [PASS]
ok 1 ksm_tests -N -m 1
---------------------------
running ./ksm_tests -N -m 0
---------------------------
mbind: Invalid argument
not ok 1 KSM NUMA merging
Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0 [FAIL]
not ok 2 ksm_tests -N -m 0 # exit=1

After patch:
---------------------------
running ./ksm_tests -N -m 1
---------------------------
At least 2 NUMA nodes with memory must be available ok 1
SKIP KSM NUMA merging
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0 [PASS]
ok 1 ksm_tests -N -m 1
---------------------------
running ./ksm_tests -N -m 0
---------------------------
At least 2 NUMA nodes with memory must be available ok 1
SKIP KSM NUMA merging
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0 [PASS]
ok 2 ksm_tests -N -m 0

---
 tools/testing/selftests/mm/ksm_tests.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

index a050f4840cfa..2ebbb544c671 100644
@@ -440,9 +440,9 @@ static int get_next_mem_node(int node)
 		mem_node = i % (max_node + 1);
 		node_size = numa_node_size(mem_node, NULL);
 		if (node_size > 0)
-			break;
+			return mem_node;
 	}
-	return mem_node;
+	return -ENODEV;
 }
 
 static int get_first_mem_node(void)

@@ -455,8 +455,8 @@ static int check_ksm_numa_merge(int merge_type, int mapping, int prot, int timeo
 {
 	void *numa1_map_ptr, *numa2_map_ptr;
 	struct timespec start_time;
+	int first_node, second_node;
 	int page_count = 2;
-	int first_node;
 
 	if (clock_gettime(CLOCK_MONOTONIC_RAW, &start_time)) {
 		ksft_perror("clock_gettime");

@@ -467,17 +467,19 @@ static int check_ksm_numa_merge(int merge_type, int mapping, int prot, int timeo
 		ksft_print_msg("NUMA support not enabled\n");
 		return KSFT_SKIP;
 	}
-	if (numa_num_configured_nodes() <= 1) {
-		ksft_print_msg("At least 2 NUMA nodes must be available\n");
+	first_node = get_first_mem_node();
+	second_node = get_next_mem_node(first_node);
+
+	if (second_node < 0) {
+		ksft_print_msg("At least 2 NUMA nodes with memory must be available\n");
 		return KSFT_SKIP;
 	}
 	if (ksm_write_sysfs(KSM_FP("merge_across_nodes"), merge_across_nodes))
 		return KSFT_FAIL;
 
 	/* allocate 2 pages in 2 different NUMA nodes and fill them with the same data */
-	first_node = get_first_mem_node();
 	numa1_map_ptr = numa_alloc_onnode(page_size, first_node);
-	numa2_map_ptr = numa_alloc_onnode(page_size, get_next_mem_node(first_node));
+	numa2_map_ptr = numa_alloc_onnode(page_size, second_node);
 	if (!numa1_map_ptr || !numa2_map_ptr) {
 		ksft_perror("numa_alloc_onnode");
 		return KSFT_FAIL;

2.52.0

Some MM selftests attempt to configure the amount of HugeTLB pages of different sizes by writing to nr_hugepages.

PowerPC hash MMU pSeries systems advertise gigantic hugepage sizes but do not support runtime allocation of such pages, writes to the corresponding nr_hugepages file fail with -EINVAL. This causes the test to bail out even though the failure is due to a platform limitation rather than the
functionality being tested.

Ignore -EINVAL when configuring nr_hugepages so that tests continue to run on systems where gigantic hugepage allocation is unsupported.

Before patch:
-------------------------
running ./hugetlb-madvise
-------------------------
TAP version 13
1..1
[INFO] detected hugetlb page size: 16777216 KiB
[INFO] detected hugetlb page size: 16384 KiB
ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 Bail out! /sys/kernel/mm/hugepages/hugepages-16777216kB/nr_hugepages write(0) failed: Invalid argument
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:0 error:0 [FAIL]

After patch:
-------------------------
running ./hugetlb-madvise
-------------------------
TAP version 13
1..1
[INFO] detected hugetlb page size: 16777216 KiB [INFO] detected hugetlb page size: 16384 KiB
ok 1 MADV_DONTNEED and MADV_REMOVE on hugetlb
Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0 [PASS]

---
 .../testing/selftests/mm/hugepage_settings.c  |  2 +-
 tools/testing/selftests/mm/vm_util.c          | 26 ++++++++++++++++---
 tools/testing/selftests/mm/vm_util.h          |  1 +
 3 files changed, 24 insertions(+), 5 deletions(-)

index 2eab2110ac6a..d7917dce3aba 100644
@@ -437,7 +437,7 @@ void hugetlb_set_nr_pages(unsigned long size, unsigned long nr)
 
 	hugetlb_sysfs_path(path, sizeof(path), size, "nr_hugepages");
 
-	write_num(path, nr);
+	write_num_ignore_einval(path, nr);
 }
 
 unsigned long hugetlb_free_pages(unsigned long size)

index 311fc5b4513e..ef1ea11981a7 100644
@@ -719,7 +719,7 @@ int read_file(const char *path, char *buf, size_t buflen)
 	return (unsigned int) numread;
 }
 
-void write_file(const char *path, const char *buf, size_t buflen)
+static void __write_file(const char *path, const char *buf, size_t buflen, bool ignore_einval)
 {
 	int fd, saved_errno;
 	ssize_t numwritten;

@@ -735,14 +735,22 @@ void write_file(const char *path, const char *buf, size_t buflen)
 	saved_errno = errno;
 	close(fd);
 	errno = saved_errno;
-	if (numwritten < 0)
+	if (numwritten < 0) {
+		if (ignore_einval && errno == EINVAL)
+			return;
 		ksft_exit_fail_msg("%s write(%.*s) failed: %s\n", path, (int)(buflen - 1),
 				buf, strerror(errno));
+	}
 	if (numwritten != buflen - 1)
 		ksft_exit_fail_msg("%s write(%.*s) is truncated, expected %zu bytes, got %zd bytes\n",
 				path, (int)(buflen - 1), buf, buflen - 1, numwritten);
 }
 
+void write_file(const char *path, const char *buf, size_t buflen)
+{
+	__write_file(path, buf, buflen, /* ignore_einval = */ false);
+}
+
 unsigned long read_num(const char *path)
 {
 	char buf[21];

@@ -753,12 +761,22 @@ unsigned long read_num(const char *path)
 	return strtoul(buf, NULL, 10);
 }
 
-void write_num(const char *path, unsigned long num)
+static void __write_num(const char *path, unsigned long num, bool ignore_einval)
 {
 	char buf[21];
 
 	sprintf(buf, "%lu", num);
-	write_file(path, buf, strlen(buf) + 1);
+	__write_file(path, buf, strlen(buf) + 1, ignore_einval);
+}
+
+void write_num(const char *path, unsigned long num)
+{
+	return __write_num(path, num, /* ignore_einval = */ false);
+}
+
+void write_num_ignore_einval(const char *path, unsigned long num)
+{
+	return __write_num(path, num, /* ignore_einval = */ true);
 }
 
 static unsigned long shmall, shmmax;

index ea8fc8fdf0eb..7799154b67ee 100644
@@ -168,6 +168,7 @@ void write_file(const char *path, const char *buf, size_t buflen);
 int read_file(const char *path, char *buf, size_t buflen);
 unsigned long read_num(const char *path);
 void write_num(const char *path, unsigned long num);
+void write_num_ignore_einval(const char *path, unsigned long num);
 
 void shm_limits_prepare(unsigned long length);
 void __shm_limits_restore(void);

2.52.0

The KSM selftest uses conditional expressions to skip accesses to merge_across_nodes on systems without NUMA support. However, the ternary operator is combined with logical OR without parentheses:

a || numa_available() ? 0 : b || c

Due to operator precedence rules, this is parsed as:

(a || numa_available()) ? 0 : (b || c)

instead of the intended:

a || (numa_available() ? 0 : b) || c

Add parentheses around the conditional expressions to ensure the correct evaluation order.

---
 tools/testing/selftests/mm/ksm_tests.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

index 2ebbb544c671..5fd7792a0d47 100644
@@ -288,8 +288,8 @@ static bool assert_ksm_pages_count(long dupl_page_count)
 static int ksm_save_def(struct ksm_sysfs *ksm_sysfs)
 {
 	if (ksm_read_sysfs(KSM_FP("max_page_sharing"), &ksm_sysfs->max_page_sharing) ||
-	    numa_available() ? 0 :
-		ksm_read_sysfs(KSM_FP("merge_across_nodes"), &ksm_sysfs->merge_across_nodes) ||
+	    (numa_available() ? 0 :
+		ksm_read_sysfs(KSM_FP("merge_across_nodes"), &ksm_sysfs->merge_across_nodes)) ||
 	    ksm_read_sysfs(KSM_FP("sleep_millisecs"), &ksm_sysfs->sleep_millisecs) ||
 	    ksm_read_sysfs(KSM_FP("pages_to_scan"), &ksm_sysfs->pages_to_scan) ||
 	    ksm_read_sysfs(KSM_FP("run"), &ksm_sysfs->run) ||

@@ -304,8 +304,8 @@ static int ksm_save_def(struct ksm_sysfs *ksm_sysfs)
 static int ksm_restore(struct ksm_sysfs *ksm_sysfs)
 {
 	if (ksm_write_sysfs(KSM_FP("max_page_sharing"), ksm_sysfs->max_page_sharing) ||
-	    numa_available() ? 0 :
-		ksm_write_sysfs(KSM_FP("merge_across_nodes"), ksm_sysfs->merge_across_nodes) ||
+	    (numa_available() ? 0 :
+		ksm_write_sysfs(KSM_FP("merge_across_nodes"), ksm_sysfs->merge_across_nodes)) ||
 	    ksm_write_sysfs(KSM_FP("pages_to_scan"), ksm_sysfs->pages_to_scan) ||
 	    ksm_write_sysfs(KSM_FP("run"), ksm_sysfs->run) ||
 	    ksm_write_sysfs(KSM_FP("sleep_millisecs"), ksm_sysfs->sleep_millisecs) ||

@@ -846,8 +846,8 @@ int main(int argc, char *argv[])
 
 	if (ksm_write_sysfs(KSM_FP("run"), 2) ||
 	    ksm_write_sysfs(KSM_FP("sleep_millisecs"), 0) ||
-	    numa_available() ? 0 :
-		ksm_write_sysfs(KSM_FP("merge_across_nodes"), 1) ||
+	    (numa_available() ? 0 :
+		ksm_write_sysfs(KSM_FP("merge_across_nodes"), 1)) ||
 	    ksm_write_sysfs(KSM_FP("pages_to_scan"), page_count))
 		ksft_exit_fail_msg("Cannot set up KSM tunables\n");
 

2.52.0

LGTM. Using proper flags would maybe be nicer, but no need for that for this corner case for now.

Cheers,

David

Thanks. AI review asked one question:

	https://sashiko.dev/#/patchset/[email protected]

Hi Andrew,
I answered this in v2, as the same question was raised by Sashiko:
https://lore.kernel.org/all/[email protected]/

Thanks,
Sayali