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From: Kip Macy <kmacy@FreeBSD.org>
To: Perforce Change Reviews <perforce@freebsd.org>
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Subject: PERFORCE change 126348 for review
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http://perforce.freebsd.org/chv.cgi?CH=126348

Change 126348 by kmacy@kmacy_home:ethng on 2007/09/13 01:27:50

	remove bogus assert preventing recursion
	be extra paranoid about volatile when doing adaptive spinning 

Affected files ...

.. //depot/projects/ethng/src/sys/kern/kern_rwlock.c#2 edit

Differences ...

==== //depot/projects/ethng/src/sys/kern/kern_rwlock.c#2 (text+ko) ====

@@ -186,9 +186,6 @@
 	MPASS(curthread != NULL);
 	KASSERT(rw->rw_lock != RW_DESTROYED,
 	    ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
-	KASSERT(rw_wowner(rw) != curthread,
-	    ("%s (%s): wlock already held @ %s:%d", __func__,
-	    rw->lock_object.lo_name, file, line));
 	WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 	    line);
 	__rw_wlock(rw, curthread, file, line);
@@ -327,7 +324,7 @@
 		 * the owner stops running or the state of the lock
 		 * changes.
 		 */
-		owner = (struct thread *)RW_OWNER(x);
+		owner = (volatile struct thread *)RW_OWNER(x);
 		if (TD_IS_RUNNING(owner)) {
 			turnstile_cancel(ts);
 			if (LOCK_LOG_TEST(&rw->lock_object, 0))
@@ -337,13 +334,16 @@
 			lock_profile_obtain_lock_failed(&rw->lock_object,
 			    &contested, &waittime);
 #endif
-			while ((struct thread*)RW_OWNER(rw->rw_lock)== owner &&
-			    TD_IS_RUNNING(owner))
+			if (owner == curthread)
+				panic("logic error in rwlock");
+			while ((volatile struct thread*)RW_OWNER(rw->rw_lock)== owner &&
+			    TD_IS_RUNNING(owner)) 
 				cpu_spinwait();
+
 			continue;
+
 		}
 #endif
-
 		/*
 		 * We were unable to acquire the lock and the read waiters
 		 * flag is set, so we must block on the turnstile.