[LTP] [PATCH v12] semctl01: fix SEM_STAT failures under parallel LTP runs

[Stephen Bertram]

SEM_STAT relied on the global high index from IPC_INFO to find this
test's semaphore set. That index is not stable when other IPC tests run
concurrently, and could trigger TBROK aborts under parallel LTP runs.
Look up the index for this test's own semaphore set instead.

This also updates func_iinfo(), which no longer derives sem_index, and
tightens func_sstat() to compare the returned id against sem_id.

Signed-off-by: Stephen Bertram <sbertram@redhat.com>
---
Test: ./kirk -w 4 -f syscalls_32 -p semctl01 -i 1000

Before changes:
Total runs:  32000
Runtime:    16m 32s
Passed:     415968
Failed:     0
Skipped:    0
Broken:     16
Warnings:   0

After changes:
Total runs:  32000
Runtime:    16m 35s
Passed:     416000
Failed:     0
Skipped:    0
Broken:     0
Warnings:   0

Assisted-by: Cursor

 testcases/kernel/syscalls/semctl/semctl01.c | 66 +++++++++++++++++----
 1 file changed, 55 insertions(+), 11 deletions(-)

diff --git a/testcases/kernel/syscalls/semctl/semctl01.c b/testcases/kernel/syscalls/semctl/semctl01.c
index 5bd675ab6..717d005a8 100644
--- a/testcases/kernel/syscalls/semctl/semctl01.c
+++ b/testcases/kernel/syscalls/semctl/semctl01.c
@@ -210,13 +210,16 @@ static void func_rmid(void)
 
 static void func_iinfo(int hidx)
 {
-	if (hidx >= 0) {
-		sem_index = hidx;
-		tst_res(TPASS, "the highest index is correct");
-	} else {
-		sem_index = 0;
-		tst_res(TFAIL, "the highest index is incorrect");
-	}
+	/*
+	 * Return value is the highest used index. Our set is alive, so the
+	 * highest used index must be at least our index.
+	 */
+	if (hidx >= sem_index)
+		tst_res(TPASS, "IPC_INFO highest index %d >= our index %d",
+			hidx, sem_index);
+	else
+		tst_res(TFAIL, "IPC_INFO highest index %d < our index %d",
+			hidx, sem_index);
 }
 
 static void func_sinfo(void)
@@ -227,12 +230,47 @@ static void func_sinfo(void)
 		tst_res(TPASS, "number of semaphore sets is correct");
 }
 
-static void func_sstat(int semidx)
+/*
+ * get_sem_idx_from_id() relies on this same identity (SEM_STAT(i) == id)
+ * to find sem_index during setup. Re-checking it here still has
+ * meaning: it verifies that SEM_STAT still resolves to our set at
+ * test-execution time, catching the case where a parallel IPC test
+ * reused sem_index in between - the exact race this patch fixes.
+ */
+static void func_sstat(int semid)
 {
-	if (semidx >= 0)
+	if (semid == sem_id)
 		tst_res(TPASS, "id of the semaphore set is correct");
 	else
-		tst_res(TFAIL, "id of the semaphore set is incorrect");
+		tst_res(TFAIL, "expected sem_id %d, got %d", sem_id, semid);
+}
+
+/*
+ * SEM_STAT takes an index into the kernel's internal array, not a semid.
+ * Return the index that maps to this test's set.
+ */
+static int get_sem_idx_from_id(int id)
+{
+	struct seminfo info;
+	struct semid_ds dummy_ds;
+	union semun arg;
+	int max_idx, i;
+
+	arg.__buf = &info;
+	/* SEM_INFO ignores semid; but SAFE_SEMCTL requires an lvalue */
+	max_idx = SAFE_SEMCTL(id, 0, SEM_INFO, arg);
+
+	arg.buf = &dummy_ds;
+	for (i = 0; i <= max_idx; i++) {
+		/*
+		 * Bare semctl: unused/unreadable indices fail with
+		 * EINVAL/EACCES; SAFE_SEMCTL would abort the test.
+		 */
+		if (semctl(i, 0, SEM_STAT, arg) == id)
+			return i;
+	}
+
+	return -1;
 }
 
 static struct tcases {
@@ -263,8 +301,14 @@ static void verify_semctl(unsigned int n)
 	struct tcases *tc = &tests[n];
 	int rval;
 
-	if (sem_id == -1)
+	if (sem_id == -1) {
 		sem_id = SAFE_SEMGET(IPC_PRIVATE, PSEMS, IPC_CREAT | IPC_EXCL | SEM_RA);
+		sem_index = get_sem_idx_from_id(sem_id);
+		if (sem_index < 0)
+			tst_brk(TBROK,
+				"Failed to get sem_id %d to idx mapping", sem_id);
+		tst_res(TINFO, "sem_id=%d maps to kernel index=%d", sem_id, sem_index);
+	}
 	if (tc->func_setup) {
 		switch (tc->cmd) {
 		case GETNCNT:
-- 
2.55.0