Fix potential lost wakeup in cv_wait(_timed). (#673)

Co-authored-by: Krystian Bacławski <[email protected]>

sys/kern/condvar.c

@@ -1,6 +1,7 @@
 #include <sys/condvar.h>
 #include <sys/sleepq.h>
 #include <sys/sched.h>
+#include <sys/interrupt.h>
 #include <sys/lock.h>
 
 void cv_init(condvar_t *cv, const char *name) {
@@ -9,17 +10,20 @@ void cv_init(condvar_t *cv, const char *name) {
 }
 
 void cv_wait(condvar_t *cv, lock_t m) {
-  WITH_NO_PREEMPTION {
+  WITH_INTR_DISABLED {
     cv->waiters++;
     lk_release(m);
+    /* If we got interrupted here and an interrupt filter called
+     * cv_signal, we would have a lost wakeup, so we need interrupts
+     * to be disabled. Same goes for cv_wait_timed. */
     sleepq_wait(cv, __caller(0));
   }
   lk_acquire(m, __caller(0));
 }
 
 int cv_wait_timed(condvar_t *cv, lock_t m, systime_t timeout) {
   int status;
-  WITH_NO_PREEMPTION {
+  WITH_INTR_DISABLED {
     cv->waiters++;
     lk_release(m);
     status = sleepq_wait_timed(cv, __caller(0), timeout);