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From: John Baldwin <jhb@FreeBSD.org>
To: Perforce Change Reviews <perforce@freebsd.org>
Cc: 
Subject: PERFORCE change 82421 for review
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http://perforce.freebsd.org/chv.cgi?CH=82421

Change 82421 by jhb@jhb_slimer on 2005/08/22 20:30:35

	Merge in some more anti-foot shooting from jhb_lock.

Affected files ...

.. //depot/projects/smpng/sys/kern/kern_mutex.c#103 edit

Differences ...

==== //depot/projects/smpng/sys/kern/kern_mutex.c#103 (text+ko) ====

@@ -412,6 +412,9 @@
 	int rval;
 
 	MPASS(curthread != NULL);
+	KASSERT(m->mtx_object.lo_class == &lock_class_mtx_sleep,
+	    ("mtx_trylock() of spin mutex %s @ %s:%d", m->mtx_object.lo_name,
+	    file, line));
 
 	if (mtx_owned(m) && (m->mtx_object.lo_flags & LO_RECURSABLE) != 0) {
 		m->mtx_recurse++;
@@ -460,6 +463,15 @@
 		return;
 	}
 
+	/*
+	 * If we have already panic'd and this is the thread that called
+	 * panic(), then don't block on any mutexes but silently succeed.
+	 * Otherwise, the kernel will deadlock since the scheduler isn't
+	 * going to run the thread that holds the lock we need.
+	 */
+	if (panicstr != NULL && curthread->td_flags & TDF_INPANIC)
+		return;
+
 	if (LOCK_LOG_TEST(&m->mtx_object, opts))
 		CTR4(KTR_LOCK,
 		    "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
@@ -607,7 +619,7 @@
 			}
 			if (i < 60000000)
 				DELAY(1);
-			else if (!kdb_active) {
+			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);
 #ifdef WITNESS
@@ -654,6 +666,15 @@
 		return;
 	}
 
+	/*
+	 * If we failed to unlock this lock and we are a thread that has
+	 * called panic(), it may be due to the bypass in _mtx_lock_sleep()
+	 * above.  In that case, just return and leave the lock alone to
+	 * avoid changing the state.
+	 */
+	if (panicstr != NULL && curthread->td_flags & TDF_INPANIC)
+		return;
+
 	turnstile_lock(&m->mtx_object);
 	ts = turnstile_lookup(&m->mtx_object);
 	if (LOCK_LOG_TEST(&m->mtx_object, opts))