From: David Edmondson <david.edmond...@oracle.com>
Test that downgrading an rwlock does not result in a failure to
schedule coroutines queued on the rwlock.
The diagram associated with test_co_rwlock_downgrade() describes the
intended behaviour, but what was observed previously corresponds to:
| c1 | c2 | c3 | c4 |
|--------+------------+------------+----------|
| rdlock | | | |
| yield | | | |
| | wrlock | | |
| | <queued> | | |
| | | rdlock | |
| | | <queued> | |
| | | | wrlock |
| | | | <queued> |
| unlock | | | |
| yield | | | |
| | <dequeued> | | |
| | downgrade | | |
| | ... | | |
| | unlock | | |
| | | <dequeued> | |
| | | <queued> | |
This results in a failure...
ERROR:../tests/test-coroutine.c:369:test_co_rwlock_downgrade: assertion failed:
(c3_done)
Bail out! ERROR:../tests/test-coroutine.c:369:test_co_rwlock_downgrade:
assertion failed: (c3_done)
...as a result of the c3 coroutine failing to run to completion.
Signed-off-by: David Edmondson <david.edmond...@oracle.com>
Message-Id: <20210309144015.557477-5-david.edmond...@oracle.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
tests/unit/test-coroutine.c | 99 +++++++++++++++++++++++++++++++++++++
1 file changed, 99 insertions(+)
diff --git a/tests/unit/test-coroutine.c b/tests/unit/test-coroutine.c
index 6e6f51d480..aa77a3bcb3 100644
--- a/tests/unit/test-coroutine.c
+++ b/tests/unit/test-coroutine.c
@@ -325,6 +325,104 @@ static void test_co_rwlock_upgrade(void)
g_assert(c2_done);
}
+static void coroutine_fn rwlock_rdlock_yield(void *opaque)
+{
+ qemu_co_rwlock_rdlock(&rwlock);
+ qemu_coroutine_yield();
+
+ qemu_co_rwlock_unlock(&rwlock);
+ qemu_coroutine_yield();
+
+ *(bool *)opaque = true;
+}
+
+static void coroutine_fn rwlock_wrlock_downgrade(void *opaque)
+{
+ qemu_co_rwlock_wrlock(&rwlock);
+
+ qemu_co_rwlock_downgrade(&rwlock);
+ qemu_co_rwlock_unlock(&rwlock);
+ *(bool *)opaque = true;
+}
+
+static void coroutine_fn rwlock_rdlock(void *opaque)
+{
+ qemu_co_rwlock_rdlock(&rwlock);
+
+ qemu_co_rwlock_unlock(&rwlock);
+ *(bool *)opaque = true;
+}
+
+static void coroutine_fn rwlock_wrlock(void *opaque)
+{
+ qemu_co_rwlock_wrlock(&rwlock);
+
+ qemu_co_rwlock_unlock(&rwlock);
+ *(bool *)opaque = true;
+}
+
+/*
+ * Check that downgrading a reader-writer lock does not cause a hang.
+ *
+ * Four coroutines are used to produce a situation where there are
+ * both reader and writer hopefuls waiting to acquire an rwlock that
+ * is held by a reader.
+ *
+ * The correct sequence of operations we aim to provoke can be
+ * represented as:
+ *
+ * | c1 | c2 | c3 | c4 |
+ * |--------+------------+------------+------------|
+ * | rdlock | | | |
+ * | yield | | | |
+ * | | wrlock | | |
+ * | | <queued> | | |
+ * | | | rdlock | |
+ * | | | <queued> | |
+ * | | | | wrlock |
+ * | | | | <queued> |
+ * | unlock | | | |
+ * | yield | | | |
+ * | | <dequeued> | | |
+ * | | downgrade | | |
+ * | | | <dequeued> | |
+ * | | | unlock | |
+ * | | ... | | |
+ * | | unlock | | |
+ * | | | | <dequeued> |
+ * | | | | unlock |
+ */
+static void test_co_rwlock_downgrade(void)
+{
+ bool c1_done = false;
+ bool c2_done = false;
+ bool c3_done = false;
+ bool c4_done = false;
+ Coroutine *c1, *c2, *c3, *c4;
+
+ qemu_co_rwlock_init(&rwlock);
+
+ c1 = qemu_coroutine_create(rwlock_rdlock_yield, &c1_done);
+ c2 = qemu_coroutine_create(rwlock_wrlock_downgrade, &c2_done);
+ c3 = qemu_coroutine_create(rwlock_rdlock, &c3_done);
+ c4 = qemu_coroutine_create(rwlock_wrlock, &c4_done);
+
+ qemu_coroutine_enter(c1);
+ qemu_coroutine_enter(c2);
+ qemu_coroutine_enter(c3);
+ qemu_coroutine_enter(c4);
+
+ qemu_coroutine_enter(c1);
+
+ g_assert(c2_done);
+ g_assert(c3_done);
+ g_assert(c4_done);
+
+ qemu_coroutine_enter(c1);
+
+ g_assert(c1_done);
+}
+
/*
* Check that creation, enter, and return work
*/
@@ -563,6 +661,7 @@ int main(int argc, char **argv)
g_test_add_func("/locking/co-mutex", test_co_mutex);
g_test_add_func("/locking/co-mutex/lockable", test_co_mutex_lockable);
g_test_add_func("/locking/co-rwlock/upgrade", test_co_rwlock_upgrade);
+ g_test_add_func("/locking/co-rwlock/downgrade", test_co_rwlock_downgrade);
if (g_test_perf()) {
g_test_add_func("/perf/lifecycle", perf_lifecycle);
g_test_add_func("/perf/nesting", perf_nesting);
--
2.29.2
