diff mbox series

[RFC,v2,4/4] selftests/rseq: Implement rseq_mutex test program

Message ID 20230529191416.53955-5-mathieu.desnoyers@efficios.com
State New
Headers
Series Extend rseq with sched_state_ptr field |

Commit Message

Mathieu Desnoyers May 29, 2023, 7:14 p.m. UTC 
  Example use of the rseq sched state.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 tools/testing/selftests/rseq/.gitignore   |   1 +
 tools/testing/selftests/rseq/Makefile     |   3 +-
 tools/testing/selftests/rseq/rseq_mutex.c | 120 ++++++++++++++++++++++
 3 files changed, 123 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/rseq/rseq_mutex.c

Comments

Thomas Gleixner Sept. 28, 2023, 7:55 p.m. UTC | #1 
On Mon, May 29 2023 at 15:14, Mathieu Desnoyers wrote:
> +static void rseq_lock_slowpath(struct rseq_mutex *lock)
> +{
> +	int i = 0;
> +
> +	for (;;) {
> +		struct rseq_abi_sched_state *expected = NULL, *self = rseq_get_sched_state(rseq_get_abi());
> +
> +		if (__atomic_compare_exchange_n(&lock->owner, &expected, self, false,
> +						__ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
> +			break;
> +		//TODO: use rseq critical section to protect dereference of owner thread's
> +		//rseq_abi_sched_state, combined with rseq fence at thread reclaim.
> +		if ((RSEQ_READ_ONCE(expected->state) & RSEQ_ABI_SCHED_STATE_FLAG_ON_CPU) &&

For robust and PI futexes the futex value is an ABI between kernel and
user space. Sure, this is only meant for demonstration, but it's the
wrong direction.

Thanks,

        tglx
diff mbox series

Patch

diff --git a/tools/testing/selftests/rseq/.gitignore b/tools/testing/selftests/rseq/.gitignore
index a8db9f7a7cec..38d5b2fe5905 100644
--- a/tools/testing/selftests/rseq/.gitignore
+++ b/tools/testing/selftests/rseq/.gitignore
@@ -10,3 +10,4 @@  param_test_mm_cid
 param_test_mm_cid_benchmark
 param_test_mm_cid_compare_twice
 sched_state_test
+rseq_mutex
diff --git a/tools/testing/selftests/rseq/Makefile b/tools/testing/selftests/rseq/Makefile
index 7c8f4f2be74c..a9d7ceb5b79b 100644
--- a/tools/testing/selftests/rseq/Makefile
+++ b/tools/testing/selftests/rseq/Makefile
@@ -14,7 +14,8 @@  OVERRIDE_TARGETS = 1
 
 TEST_GEN_PROGS = basic_test basic_percpu_ops_test basic_percpu_ops_mm_cid_test param_test \
 		param_test_benchmark param_test_compare_twice param_test_mm_cid \
-		param_test_mm_cid_benchmark param_test_mm_cid_compare_twice sched_state_test
+		param_test_mm_cid_benchmark param_test_mm_cid_compare_twice sched_state_test \
+		rseq_mutex
 
 TEST_GEN_PROGS_EXTENDED = librseq.so
 
diff --git a/tools/testing/selftests/rseq/rseq_mutex.c b/tools/testing/selftests/rseq/rseq_mutex.c
new file mode 100644
index 000000000000..01afd6a0e8bd
--- /dev/null
+++ b/tools/testing/selftests/rseq/rseq_mutex.c
@@ -0,0 +1,120 @@ 
+// SPDX-License-Identifier: LGPL-2.1
+
+#define _GNU_SOURCE
+#include <assert.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/time.h>
+#include <poll.h>
+
+#include "rseq.h"
+
+#define RSEQ_MUTEX_MAX_BUSY_LOOP	100
+
+struct rseq_mutex {
+	/*
+	 * When non-NULL, owner points to per-thread rseq_abi_sched_state of
+	 * owner thread.
+	 */
+	struct rseq_abi_sched_state *owner;
+};
+
+static struct rseq_mutex lock = { .owner = NULL };
+
+static int testvar;
+
+static void rseq_lock_slowpath(struct rseq_mutex *lock)
+{
+	int i = 0;
+
+	for (;;) {
+		struct rseq_abi_sched_state *expected = NULL, *self = rseq_get_sched_state(rseq_get_abi());
+
+		if (__atomic_compare_exchange_n(&lock->owner, &expected, self, false,
+						__ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+			break;
+		//TODO: use rseq critical section to protect dereference of owner thread's
+		//rseq_abi_sched_state, combined with rseq fence at thread reclaim.
+		if ((RSEQ_READ_ONCE(expected->state) & RSEQ_ABI_SCHED_STATE_FLAG_ON_CPU) &&
+		    i < RSEQ_MUTEX_MAX_BUSY_LOOP) {
+			rseq_barrier();			/* busy-wait, e.g. cpu_relax(). */
+			i++;
+		} else {
+			//TODO: Enqueue waiter in a wait-queue, and integrate
+			//with sys_futex rather than waiting for 10ms.
+			(void) poll(NULL, 0, 10);	/* wait 10ms */
+		}
+	}
+}
+
+static void rseq_lock(struct rseq_mutex *lock)
+{
+	struct rseq_abi_sched_state *expected = NULL, *self = rseq_get_sched_state(rseq_get_abi());
+
+	if (__atomic_compare_exchange_n(&lock->owner, &expected, self, false,
+					__ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+		return;
+	rseq_lock_slowpath(lock);
+}
+
+static void rseq_unlock(struct rseq_mutex *lock)
+{
+	__atomic_store_n(&lock->owner, NULL, __ATOMIC_RELEASE);
+	//TODO: integrate with sys_futex and wakeup oldest waiter.
+}
+
+static
+void *test_thread(void *arg)
+{
+	int i;
+
+	if (rseq_register_current_thread()) {
+		fprintf(stderr, "Error: rseq_register_current_thread(...) failed(%d): %s\n",
+			errno, strerror(errno));
+		abort();
+	}
+
+	for (i = 0; i < 1000; i++) {
+		int var;
+
+		rseq_lock(&lock);
+		var = RSEQ_READ_ONCE(testvar);
+		if (var) {
+			fprintf(stderr, "Unexpected value %d\n", var);
+			abort();
+		}
+		RSEQ_WRITE_ONCE(testvar, 1);
+		if (!(i % 10))
+			(void) poll(NULL, 0, 10);
+		else
+			rseq_barrier();
+		RSEQ_WRITE_ONCE(testvar, 0);
+		rseq_unlock(&lock);
+	}
+
+	if (rseq_unregister_current_thread()) {
+		fprintf(stderr, "Error: rseq_unregister_current_thread(...) failed(%d): %s\n",
+			errno, strerror(errno));
+		abort();
+	}
+	return NULL;
+}
+
+int main(int argc, char **argv)
+{
+	int nr_threads = 5;
+	pthread_t test_thread_id[nr_threads];
+	int i;
+
+	for (i = 0; i < nr_threads; i++) {
+		pthread_create(&test_thread_id[i], NULL, test_thread, NULL);
+	}
+
+	for (i = 0; i < nr_threads; i++) {
+		pthread_join(test_thread_id[i], NULL);
+	}
+
+	return 0;
+}