Possible deadlock issues

[ryancaicse]

Hi, it seems that lock device->sync_mutex is missed to be released after 248. In the while loop, the lock could be acquired twice and a deadlock occurs.

cen64/device/device.c

Lines 230 to 256 in 1b31ca9

	while (likely(device->running)) {
	unsigned i, j;
	for (i = 0; i < 6250 / 2; i++) {
	for (j = 0; j < 2; j++) {
	ai_cycle(&device->ai);
	pi_cycle(&device->pi);
	}
	for (j = 0; j < 3; j++)
	vr4300_cycle(device->vr4300);
	}
	// Sync up with the RCP thread.
	cen64_mutex_lock(&device->sync_mutex);
	if (!device->other_thread_is_waiting) {
	device->other_thread_is_waiting = true;
	cen64_cv_wait(&device->sync_cv, &device->sync_mutex);
	}
	else {
	device->other_thread_is_waiting = false;
	cen64_mutex_unlock(&device->sync_mutex);
	cen64_cv_signal(&device->sync_cv);
	}
	}

[ryancaicse]

Here is another one similar to the above.

cen64/device/device.c

Lines 230 to 255 in 1b31ca9

	while (likely(device->running)) {
	unsigned i, j;
	for (i = 0; i < 6250 / 2; i++) {
	for (j = 0; j < 2; j++) {
	ai_cycle(&device->ai);
	pi_cycle(&device->pi);
	}
	for (j = 0; j < 3; j++)
	vr4300_cycle(device->vr4300);
	}
	// Sync up with the RCP thread.
	cen64_mutex_lock(&device->sync_mutex);
	if (!device->other_thread_is_waiting) {
	device->other_thread_is_waiting = true;
	cen64_cv_wait(&device->sync_cv, &device->sync_mutex);
	}
	else {
	device->other_thread_is_waiting = false;
	cen64_mutex_unlock(&device->sync_mutex);
	cen64_cv_signal(&device->sync_cv);
	}

[ryancaicse]

Could anyone take a look? thanks

[tj90241]

This is expected... see the manpage for pthread_cond_wait:

These functions atomically release mutex and cause the calling thread to block on the condition variable cond; atomically here means "atomically with respect to access by another thread to the mutex and then the condition variable".