PERFORCE change 92336 for review

[John Baldwin]

http://perforce.freebsd.org/chv.cgi?CH=92336

Change 92336 by jhb at jhb_zion on 2006/02/24 15:08:55

	- Make the spin lock too long panic message more useful and
	  more accurate (the "5 seconds" is dubious).
	- Allow idle threads to spin on sched_lock forever.

Affected files ...

.. //depot/projects/smpng/sys/kern/kern_mutex.c#118 edit

Differences ...

==== //depot/projects/smpng/sys/kern/kern_mutex.c#118 (text+ko) ====

@@ -91,8 +91,9 @@
  */
 #define mtx_unowned(m)	((m)->mtx_lock == MTX_UNOWNED)
 
-#define mtx_owner(m)	(mtx_unowned((m)) ? NULL \
-	: (struct thread *)((m)->mtx_lock & MTX_FLAGMASK))
+#define	mtx_rawowner(m)	((struct thread *)((m)->mtx_lock & MTX_FLAGMASK))
+
+#define mtx_owner(m)	(mtx_unowned((m)) ? NULL : mtx_rawowner((m)))
 
 #ifdef DDB
 static void	db_show_mtx(struct lock_object *lock);
@@ -550,7 +551,8 @@
 		if (m != &Giant && TD_IS_RUNNING(owner)) {
 #endif
 			turnstile_release(&m->mtx_object);
-			while (mtx_owner(m) == owner && TD_IS_RUNNING(owner)) {
+			while (mtx_rawowner(m) == owner &&
+			    TD_IS_RUNNING(owner)) {
 				cpu_spinwait();
 			}
 			continue;
@@ -606,7 +608,8 @@
 _mtx_lock_spin(struct mtx *m, uintptr_t tid, int opts, const char *file,
     int line)
 {
-	int i = 0;
+	int i = 0, idlespin = 0;
+	struct thread *td;
 #ifdef __i386__
 	int apic_hack;
 #endif
@@ -614,6 +617,9 @@
 	if (LOCK_LOG_TEST(&m->mtx_object, opts))
 		CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);
 
+	/* It's ok for the idle loop to spin forever on sched_lock. */
+	if (m == &sched_lock && curthread == PCPU_GET(idlethread))
+		idlespin = 1;
 	for (;;) {
 		if (_obtain_lock(m, tid))
 			break;
@@ -630,14 +636,17 @@
 				cpu_spinwait();
 				continue;
 			}
-			if (i < 60000000)
+			if (i < 60000000 || kdb_active || panicstr != NULL ||
+			    idlespin)
 				DELAY(1);
-			else if (!kdb_active && !panicstr) {
-				printf("spin lock %s held by %p for > 5 seconds\n",
-				    m->mtx_object.lo_name, (void *)m->mtx_lock);
+			else {
+				td = mtx_owner(m);
+				printf(
+			"spin lock %p (%s) held by %p (tid %d) too long\n",
+				    m, m->mtx_object.lo_name, mtx_rawowner(m),
+				    td ? td->td_tid : -1);
 #ifdef WITNESS
-				witness_display_spinlock(&m->mtx_object,
-				    mtx_owner(m));
+				witness_display_spinlock(&m->mtx_object, td);
 #endif
 				panic("spin lock held too long");
 			}