coroutine: Assert that no locks are held on termination

A coroutine that takes a lock must also release it again. If the
coroutine terminates without having released all its locks, it's buggy
and we'll probably run into a deadlock sooner or later. Make sure that
we don't get such cases.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

include/qemu/coroutine_int.h

@@ -39,6 +39,7 @@ struct Coroutine {
     void *entry_arg;
     Coroutine *caller;
     QSLIST_ENTRY(Coroutine) pool_next;
+    size_t locks_held;
 
     /* Coroutines that should be woken up when we yield or terminate */
     QSIMPLEQ_HEAD(, Coroutine) co_queue_wakeup;

util/qemu-coroutine-lock.c

@@ -130,6 +130,7 @@ void coroutine_fn qemu_co_mutex_lock(CoMutex *mutex)
 
     mutex->locked = true;
     mutex->holder = self;
+    self->locks_held++;
 
     trace_qemu_co_mutex_lock_return(mutex, self);
 }
@@ -146,6 +147,7 @@ void coroutine_fn qemu_co_mutex_unlock(CoMutex *mutex)
 
     mutex->locked = false;
     mutex->holder = NULL;
+    self->locks_held--;
     qemu_co_queue_next(&mutex->queue);
 
     trace_qemu_co_mutex_unlock_return(mutex, self);
@@ -159,14 +161,19 @@ void qemu_co_rwlock_init(CoRwlock *lock)
 
 void qemu_co_rwlock_rdlock(CoRwlock *lock)
 {
+    Coroutine *self = qemu_coroutine_self();
+
     while (lock->writer) {
         qemu_co_queue_wait(&lock->queue);
     }
     lock->reader++;
+    self->locks_held++;
 }
 
 void qemu_co_rwlock_unlock(CoRwlock *lock)
 {
+    Coroutine *self = qemu_coroutine_self();
+
     assert(qemu_in_coroutine());
     if (lock->writer) {
         lock->writer = false;
@@ -179,12 +186,16 @@ void qemu_co_rwlock_unlock(CoRwlock *lock)
             qemu_co_queue_next(&lock->queue);
         }
     }
+    self->locks_held--;
 }
 
 void qemu_co_rwlock_wrlock(CoRwlock *lock)
 {
+    Coroutine *self = qemu_coroutine_self();
+
     while (lock->writer || lock->reader) {
         qemu_co_queue_wait(&lock->queue);
     }
     lock->writer = true;
+    self->locks_held++;
 }

util/qemu-coroutine.c

@@ -122,6 +122,7 @@ void qemu_coroutine_enter(Coroutine *co)
     case COROUTINE_YIELD:
         return;
     case COROUTINE_TERMINATE:
+        assert(!co->locks_held);
         trace_qemu_coroutine_terminate(co);
         coroutine_delete(co);
         return;