rendez: Make sure we can block before sleeping A lot of rendezvouses don't block, but any of them could. By checking in advance, instead of deep in sem_down(), we'll catch those cases where we could have blocked but rarely do. Signed-off-by: Barret Rhoden <brho@cs.berkeley.edu>

diff --git a/kern/src/rendez.c b/kern/src/rendez.c
index 576eaf6..857821c 100644
--- a/kern/src/rendez.c
+++ b/kern/src/rendez.c

@@ -22,6 +22,8 @@
 {
 	int8_t irq_state = 0;
 	struct cv_lookup_elm cle;
+
+	assert(can_block(this_pcpui_ptr()));
 	/* Do a quick check before registering and sleeping.  this is the 'check,
 	 * signal, check again' pattern, where the first check is an optimization.
 	 * Many rendezes will already be satisfied, so we want to avoid excessive
@@ -69,6 +71,7 @@
 	struct cv_lookup_elm cle;
 	struct timer_chain *pcpui_tchain = &per_cpu_info[core_id()].tchain;
 
+	assert(can_block(this_pcpui_ptr()));
 	if (!usec)
 		return;
 	/* Doing this cond check early, but then unlocking again.  Mostly just to