test/test_sref_dirty_zeroes: new test module

Actually, it's not that hard to produce dirty zeroes. Here is a test
module that does just that, and exposes a bug in the algorithm.

2 files changed, 124 insertions, 3 deletions

diff --git a/test/test_sref_dirty_zeroes.c b/test/test_sref_dirty_zeroes.c
new file mode 100644
index 00000000..2e16ffc6
--- /dev/null
+++ b/test/test_sref_dirty_zeroes.c
@@ -0,0 +1,122 @@
+/*
+ * Copyright (c) 2014 Richard Braun.
+ *
+ * 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 3 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/>.
+ *
+ *
+ * The purpose of this test module is to produce dirty zeroes and make
+ * sure they're correctly processed. It is a stress test that never ends,
+ * except on failure. Two threads are created. The first increments a
+ * scalable reference counter, then signals the second that it can decrement
+ * it. Since these threads are likely to run on different processors, a
+ * good amount of dirty zeroes should be produced, as reported by regularly
+ * printing the relevant event counters. Since the true number of references
+ * can never drop to 0, the no-reference function should never be called,
+ * and panics if it is.
+ */
+
+#include <kern/assert.h>
+#include <kern/condition.h>
+#include <kern/evcnt.h>
+#include <kern/kmem.h>
+#include <kern/macros.h>
+#include <kern/mutex.h>
+#include <kern/sprintf.h>
+#include <kern/sref.h>
+#include <kern/stddef.h>
+#include <kern/thread.h>
+#include <test/test.h>
+#include <vm/vm_kmem.h>
+
+static struct condition test_condition;
+static struct mutex test_lock;
+static struct sref_counter test_counter;
+static unsigned long test_transient_ref;
+
+static void
+test_inc(void *arg)
+{
+    volatile unsigned long i;
+    (void)arg;
+
+    for (;;) {
+        for (i = 0; i < 1000000; i++) {
+            sref_counter_inc(&test_counter);
+
+            mutex_lock(&test_lock);
+            test_transient_ref++;
+            condition_signal(&test_condition);
+
+            while (test_transient_ref != 0)
+                condition_wait(&test_condition, &test_lock);
+
+            mutex_unlock(&test_lock);
+        }
+
+        printk("counter global value: %lu\n", test_counter.value);
+        evcnt_info("sref_epoch");
+        evcnt_info("sref_dirty_zero");
+        evcnt_info("sref_true_zero");
+    }
+}
+
+static void
+test_dec(void *arg)
+{
+    (void)arg;
+
+    for (;;) {
+        mutex_lock(&test_lock);
+
+        while (test_transient_ref == 0)
+            condition_wait(&test_condition, &test_lock);
+
+        test_transient_ref--;
+        condition_signal(&test_condition);
+        mutex_unlock(&test_lock);
+
+        sref_counter_dec(&test_counter);
+    }
+}
+
+static void
+test_noref(struct sref_counter *counter)
+{
+    (void)counter;
+    panic("0 references, page released\n");
+}
+
+void
+test_setup(void)
+{
+    struct thread_attr attr;
+    struct thread *thread;
+    int error;
+
+    condition_init(&test_condition);
+    mutex_init(&test_lock);
+
+    sref_counter_init(&test_counter, test_noref);
+    test_transient_ref = 0;
+
+    thread_attr_init(&attr, "x15_test_inc");
+    thread_attr_set_detached(&attr);
+    error = thread_create(&thread, &attr, test_inc, NULL);
+    assert(!error);
+
+    thread_attr_init(&attr, "x15_test_dec");
+    thread_attr_set_detached(&attr);
+    error = thread_create(&thread, &attr, test_dec, NULL);
+    assert(!error);
+}
diff --git a/test/test_sref_noref.c b/test/test_sref_noref.c
index e58917c7..911eb61e 100644
--- a/test/test_sref_noref.c
+++ b/test/test_sref_noref.c
@@ -28,9 +28,8 @@
  * Finally, it releases the initial reference, at which point, the
  * no-reference function should be called.
  *
- * Notes:
- * The number of loops must be large enough to allow many epochs to occur.
- * Also, it's very hard to artificially produce dirty zeroes.
+ * Notes: the number of loops must be large enough to allow many epochs
+ * to occur.
  */
 
 #include <kern/assert.h>