trying to track down some race condition..

020f4b22 · Nickolai Zeldovich · 6d913c9f · 020f4b22
--- a/kernel/gc.cc
+++ b/kernel/gc.cc
@@ -51,7 +51,11 @@ gc_free_tofreelist(atomic<rcu_freed*> *head, u64 epoch)
  int nfree = 0;
  rcu_freed *r, *nr;

-  for (r = *head; r != NULL; r = nr) {
+  r = *head;
+  while (!std::atomic_compare_exchange_strong(head, &r, (rcu_freed*) 0))
+    ; /* spin */
+
+  for (; r; r = nr) {
    if (r->_rcu_epoch > epoch) {
      cprintf("gc_free_tofreelist: r->epoch %ld > epoch %ld\n", r->_rcu_epoch, epoch);
      assert(0);
@@ -60,7 +64,6 @@ gc_free_tofreelist(atomic<rcu_freed*> *head, u64 epoch)
    r->do_gc();
    nfree++;
  }
-  *head = r;
  return nfree;
 }

@@ -89,6 +92,7 @@ gc_move_to_tofree_cpu(int c, u64 epoch)
  // move delayed NEPOCH's adhead
  gc_state[c].delayed[fe].epoch += NEPOCH;
  assert(gc_state[c].delayed[fe].head == 0);
+  // XXX race with gc_delayed()?

  return 0;
 }