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From: John Baldwin <jhb@FreeBSD.org>
Subject: PERFORCE change 9529 for review
To: Perforce Change Reviews <perforce@freebsd.org>
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http://people.freebsd.org/~peter/p4db/chv.cgi?CH=9529

Change 9529 by jhb@jhb_laptop on 2002/04/10 12:15:51

	- First, fix a lock order reversal.  pgrp comes before proc.
	- Second, limcopy() can block, so release locks around the
	  limit stuff for now until the limit stuff is reworked.  Also,
	  this lets us not hold pgrpsess and pgrp locks quite so long.

Affected files ...

... //depot/projects/smpng/sys/kern/kern_fork.c#36 edit

Differences ...

==== //depot/projects/smpng/sys/kern/kern_fork.c#36 (text+ko) ====

@@ -465,10 +465,8 @@
 	    (unsigned) RANGEOF(struct ksegrp, kg_startzero, kg_endzero));
 
 	mtx_init(&p2->p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
-	PGRPSESS_XLOCK();
 	PROC_LOCK(p2);
 	PROC_LOCK(p1);
-	PGRP_LOCK(p1->p_pgrp);
 
 	bcopy(&p1->p_startcopy, &p2->p_startcopy,
 	    (unsigned) RANGEOF(struct proc, p_startcopy, p_endcopy));
@@ -556,6 +554,8 @@
 	if (p2->p_textvp)
 		VREF(p2->p_textvp);
 	p2->p_fd = fd;
+	PROC_UNLOCK(p1);
+	PROC_UNLOCK(p2);
 
 	/*
 	 * If p_limit is still copy-on-write, bump refcnt,
@@ -570,6 +570,11 @@
 		p2->p_limit->p_refcnt++;
 	}
 
+	PGRPSESS_XLOCK();
+	PGRP_LOCK(p1->p_pgrp);
+	PROC_LOCK(p2);
+	PROC_LOCK(p1);
+
 	/*
 	 * Preserve some more flags in subprocess.  PS_PROFIL has already
 	 * been preserved.
@@ -584,6 +589,7 @@
 
 	LIST_INSERT_AFTER(p1, p2, p_pglist);
 	PGRP_UNLOCK(p1->p_pgrp);
+	PGRPSESS_XUNLOCK();
 	LIST_INIT(&p2->p_children);
 	LIST_INIT(&td2->td_contested); /* XXXKSE only 1 thread? */
 
@@ -618,7 +624,6 @@
 	_PHOLD(p1);
 	PROC_UNLOCK(p1);
 	PROC_UNLOCK(p2);
-	PGRPSESS_XUNLOCK();
 
 	/*
 	 * Attach the new process to its parent.

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