bcachefs: Add a cond_resched call to the copygc main loop

We seem to have a bug where the copygc thread ends up spinning and
making the system unusable - this will at least prevent it from locking
up the machine, and it's a good thing to have anyways.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/movinggc.c

@@ -317,6 +317,8 @@ static int bch2_copygc_thread(void *arg)
 	set_freezable();
 
 	while (!kthread_should_stop()) {
+		cond_resched();
+
 		if (kthread_wait_freezable(c->copy_gc_enabled))
 			break;