[LTP] [PATCH v5 2/7] tst_atomic: Add atomic store and load tests

[Richard Palethorpe]

Similar to test09.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
---
 lib/newlib_tests/.gitignore |   1 +
 lib/newlib_tests/Makefile   |   1 +
 lib/newlib_tests/test15.c   | 142 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 144 insertions(+)
 create mode 100644 lib/newlib_tests/test15.c

diff --git a/lib/newlib_tests/.gitignore b/lib/newlib_tests/.gitignore
index 8e120074e..7d47a6531 100644
--- a/lib/newlib_tests/.gitignore
+++ b/lib/newlib_tests/.gitignore
@@ -12,6 +12,7 @@ test11
 test12
 test13
 test14
+test15
 tst_device
 tst_safe_fileops
 tst_res_hexd
diff --git a/lib/newlib_tests/Makefile b/lib/newlib_tests/Makefile
index e9976e5ba..e86d8f23a 100644
--- a/lib/newlib_tests/Makefile
+++ b/lib/newlib_tests/Makefile
@@ -7,6 +7,7 @@ LDLIBS			+= -lltp
 
 test08: CFLAGS+=-pthread
 test09: CFLAGS+=-pthread
+test15: CFLAGS+=-pthread
 
 ifeq ($(ANDROID),1)
 FILTER_OUT_MAKE_TARGETS	+= test08
diff --git a/lib/newlib_tests/test15.c b/lib/newlib_tests/test15.c
new file mode 100644
index 000000000..7563cb778
--- /dev/null
+++ b/lib/newlib_tests/test15.c
@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2017 Richard Palethorpe <rpalethorpe@suse.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * A basic regression test for tst_atomic_{load,store}. Also provides a
+ * limited check that atomic stores and loads order non-atomic memory
+ * accesses. That is, we are checking that they implement memory fences or
+ * barriers.
+ *
+ * Many architectures/machines will still pass the test even if you remove the
+ * atomic functions. X86 in particular has strong memory ordering by default
+ * so that should always pass (if you use volatile). However Aarch64
+ * (Raspberry Pi 3 Model B) has been observed to fail without the atomic
+ * functions.
+ *
+ * A failure can occur if an update to seq_n is not made globally visible by
+ * the time the next thread needs to use it.
+ */
+
+#include <stdint.h>
+#include <pthread.h>
+#include "tst_test.h"
+#include "tst_atomic.h"
+
+#define THREADS 64
+#define FILLER (1 << 20)
+
+/* Uncomment these to see what happens without atomics. To prevent the compiler
+ * from removing/reording atomic and seq_n, mark them as volatile.
+ */
+/* #define tst_atomic_load(v) (*(v)) */
+/* #define tst_atomic_store(i, v) *(v) = (i) */
+
+struct block {
+	int seq_n;
+	intptr_t id;
+	intptr_t filler[FILLER];
+};
+
+static int atomic;
+/* Instead of storing seq_n on the stack (probably next to the atomic variable
+ * above), we store it in the middle of some anonymous mapped memory and keep
+ * a pointer to it. This should decrease the probability that the value of
+ * seq_n will be synchronised between processors as a byproduct of the atomic
+ * variable being updated.
+ */
+static int *seq_n;
+static struct block *m;
+
+static void *worker_load_store(void *aid)
+{
+	int id = (intptr_t)aid, i;
+
+	for (i = tst_atomic_load(&atomic);
+	     i != id;
+	     i = tst_atomic_load(&atomic))
+		;
+
+	(m + (*seq_n))->id = id;
+	*seq_n += 1;
+	tst_atomic_store(i + 1, &atomic);
+
+	return NULL;
+}
+
+/* Attempt to stress the memory transport so that memory operations are
+ * contended and less predictable. This should increase the likelyhood of a
+ * failure if a memory fence is missing.
+ */
+static void *mem_spam(void *vp LTP_ATTRIBUTE_UNUSED)
+{
+	intptr_t i = 0, j;
+	struct block *cur = m;
+
+	tst_res(TINFO, "Memory spammer started");
+	while (tst_atomic_load(&atomic) > 0) {
+		for (j = 0; j < FILLER; j++)
+			cur->filler[j] = j;
+
+		if (i < THREADS - 1) {
+			cur = m + (++i);
+		} else {
+			i = 0;
+			cur = m;
+		}
+	}
+
+	return NULL;
+}
+
+static void do_test(void)
+{
+	intptr_t i, id;
+	pthread_t threads[THREADS + 1];
+
+	atomic = 0;
+	m = SAFE_MMAP(NULL, sizeof(*m) * THREADS,
+		      PROT_READ | PROT_WRITE,
+		      MAP_PRIVATE | MAP_ANONYMOUS,
+		      -1, 0);
+	seq_n = &((m + THREADS / 2)->seq_n);
+
+	pthread_create(&threads[THREADS], NULL, mem_spam, NULL);
+	for (i = THREADS - 1; i >= 0; i--)
+		pthread_create(&threads[i], NULL, worker_load_store, (void *)i);
+
+	for (i = 0; i < THREADS; i++) {
+		tst_res(TINFO, "Joining thread %li", i);
+		pthread_join(threads[i], NULL);
+	}
+	tst_atomic_store(-1, &atomic);
+	pthread_join(threads[THREADS], NULL);
+
+	tst_res(TINFO, "Expected\tFound");
+	for (i = 0; i < THREADS; i++) {
+		id = (m + i)->id;
+		if (id != i)
+			tst_res(TFAIL, "%d\t\t%d", (int)i, (int)id);
+		else
+			tst_res(TPASS, "%d\t\t%d", (int)i, (int)id);
+	}
+
+	SAFE_MUNMAP(m, sizeof(*m) * THREADS);
+}
+
+static struct tst_test test = {
+	.test_all = do_test,
+};
-- 
2.14.1