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 is observed currently corresponds to: | c1 | c2 | c3 | c4 | |--------+------------+------------+----------| | rdlock | | | | | yield | | | | | | wrlock | | | | | <queued> | | | | | | rdlock | | | | | <queued> | | | | | | wrlock | | | | | <queued> | | unlock | | | | | yield | | | | | | <dequeued> | | | | | downgrade | | | | | ... | | | | | unlock | | | | | | <dequeued> | | | | | <queued> | | In the test, 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> --- tests/test-coroutine.c | 112 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 112 insertions(+) diff --git a/tests/test-coroutine.c b/tests/test-coroutine.c index e946d93a65..62b0092721 100644 --- a/tests/test-coroutine.c +++ b/tests/test-coroutine.c @@ -264,6 +264,117 @@ static void test_co_mutex_lockable(void) g_assert(QEMU_MAKE_LOCKABLE(null_pointer) == NULL); } +static bool c1_done; +static bool c2_done; +static bool c3_done; +static bool c4_done; + +static void coroutine_fn rwlock_c1(void *opaque) +{ + CoRwlock *l = opaque; + + qemu_co_rwlock_rdlock(l); + qemu_coroutine_yield(); + + qemu_co_rwlock_unlock(l); + qemu_coroutine_yield(); + + c1_done = true; +} + +static void coroutine_fn rwlock_c2(void *opaque) +{ + CoRwlock *l = opaque; + + qemu_co_rwlock_wrlock(l); + + qemu_co_rwlock_downgrade(l); + qemu_co_rwlock_unlock(l); + c2_done = true; +} + +static void coroutine_fn rwlock_c3(void *opaque) +{ + CoRwlock *l = opaque; + + qemu_co_rwlock_rdlock(l); + + qemu_co_rwlock_unlock(l); + c3_done = true; +} + +static void coroutine_fn rwlock_c4(void *opaque) +{ + CoRwlock *l = opaque; + + qemu_co_rwlock_wrlock(l); + + qemu_co_rwlock_unlock(l); + c4_done = 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 | | | + * | | ... | | | + * | | unlock | | | + * | | | | <dequeued> | + * | | | | unlock | + * | | | <dequeued> | | + * | | | unlock | | + * + * Significantly, when c2 unlocks the downgraded lock, it should be c4 + * that is run rather than c3. + */ +static void test_co_rwlock_downgrade(void) +{ + CoRwlock l; + Coroutine *c1, *c2, *c3, *c4; + + qemu_co_rwlock_init(&l); + + c1 = qemu_coroutine_create(rwlock_c1, &l); + c2 = qemu_coroutine_create(rwlock_c2, &l); + c3 = qemu_coroutine_create(rwlock_c3, &l); + c4 = qemu_coroutine_create(rwlock_c4, &l); + + 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 */ @@ -501,6 +612,7 @@ int main(int argc, char **argv) g_test_add_func("/basic/order", test_order); 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/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); -- 2.30.1