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From: Roman Divacky <rdivacky@FreeBSD.org>
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Subject: PERFORCE change 113675 for review
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http://perforce.freebsd.org/chv.cgi?CH=113675

Change 113675 by rdivacky@rdivacky_witten on 2007/01/29 21:13:01

	There is no need to lock p_em in the linux_proc_init CLONE_THREAD
	case because the process cannot change the address of the p_em->shared
	because its currently running this code path. And the p_em->shared
	is the reason for synchronization here. Also protect onlu refs++
	with the emul_shared_lock as em is local to our function.

Affected files ...

.. //depot/projects/linuxolator/src/sys/compat/linux/linux_emul.c#28 edit

Differences ...

==== //depot/projects/linuxolator/src/sys/compat/linux/linux_emul.c#28 (text+ko) ====

@@ -114,13 +114,18 @@
 	if (child != 0) {
 		if (flags & CLONE_THREAD) {
 			/* lookup the parent */
-		   	EMUL_SHARED_WLOCK(&emul_shared_lock);
-			p_em = em_find(td->td_proc, EMUL_DOLOCK);
+			/* 
+			 * we dont have to lock the p_em because
+			 * its waiting for us in linux_clone so
+			 * there is no chance of it changing the
+			 * p_em->shared address
+			 */
+			p_em = em_find(td->td_proc, EMUL_DONTLOCK);
 			KASSERT(p_em != NULL, ("proc_init: parent emuldata not found for CLONE_THREAD\n"));
 			em->shared = p_em->shared;
+			EMUL_SHARED_WLOCK(&emul_shared_lock);
 			em->shared->refs++;
-		   	EMUL_SHARED_WUNLOCK(&emul_shared_lock);
-			EMUL_UNLOCK(&emul_lock);
+			EMUL_SHARED_WUNLOCK(&emul_shared_lock);
 		} else {
 			/*
 			 * handled earlier to avoid malloc(M_WAITOK) with