- Allow witness_sleep() to be called when witness hasn't been initialized

  yet.  We just return without performing any checks.
- Don't explicitly enter and exit critical sections when walking lock
  lists.  We don't need a critical section to walk the list of sleep
  locks for a thread.  We check to see if a spin lock list is empty
  before we walk it.  If the list is empty we don't need to walk it.  If
  it isn't then we already hold at least one spin lock and are already in
  a critical section and thus don't need our own explicit critical
  section.

1 files changed, 8 insertions, 16 deletions

diff --git a/sys/kern/subr_witness.c b/sys/kern/subr_witness.c
index fcc9b53..099828d 100644
--- a/sys/kern/subr_witness.c
+++ b/sys/kern/subr_witness.c
@@ -882,14 +882,9 @@ witness_sleep(int check_only, struct lock_object *lock, const char *file,
 	struct thread *td;
 	int i, n;
 
-	if (witness_dead || panicstr != NULL)
+	if (witness_cold || witness_dead || panicstr != NULL)
 		return (0);
-	KASSERT(!witness_cold, ("%s: witness_cold", __func__));
 	n = 0;
-	/*
-	 * Preemption bad because we need PCPU_PTR(spinlocks) to not change.
-	 */
-	critical_enter();
 	td = curthread;
 	lock_list = &td->td_sleeplocks;
 again:
@@ -916,7 +911,11 @@ again:
 			    lock1->li_lock->lo_name, lock1->li_file,
 			    lock1->li_line);
 		}
-	if (lock_list == &td->td_sleeplocks) {
+	if (lock_list == &td->td_sleeplocks && PCPU_GET(spinlocks) != NULL) {
+		/*
+		 * Since we already hold a spinlock preemption is
+		 * already blocked.
+		 */
 		lock_list = PCPU_PTR(spinlocks);
 		goto again;
 	}
@@ -924,7 +923,6 @@ again:
 	if (witness_ddb && n)
 		Debugger(__func__);
 #endif /* DDB */
-	critical_exit();
 	return (n);
 }
 
@@ -1346,15 +1344,9 @@ witness_list(struct thread *td)
 	 * out from under us.  It is probably best to just not try to handle
 	 * threads on other CPU's for now.
 	 */
-	if (td == curthread) {
-		/*
-		 * Preemption bad because we need PCPU_PTR(spinlocks) to not
-		 * change.
-		 */
-		critical_enter();
+	if (td == curthread && PCPU_GET(spinlocks) != NULL)
 		nheld += witness_list_locks(PCPU_PTR(spinlocks));
-		critical_exit();
-	}
+
 	return (nheld);
 }