PERFORCE change 167829 for review

[Marko Zec]

http://perforce.freebsd.org/chv.cgi?CH=167829

Change 167829 by zec at zec_tpx32 on 2009/08/26 12:00:31

	Attempt to preempt panics in vnet_alloc() call graph by doing
	a brute-force check whether a reasonable amount of kmem is
	available.  This is not guaranteed to work all the time (no
	protection against races on memory allocations), but given that
	now jail -c may fail as vnet_alloc() fails, this could serve
	as an indicator to sysadmins that an imminent panic due to
	kmem starvation may be around the corner.
	
	This is a better-than-nothing alternative to current behavior,
	which guarantees a panic on jail -c vnet when kmem is in
	short supply.

Affected files ...

.. //depot/projects/vimage-commit2/src/sys/kern/kern_jail.c#34 edit
.. //depot/projects/vimage-commit2/src/sys/net/vnet.c#6 edit

Differences ...

==== //depot/projects/vimage-commit2/src/sys/kern/kern_jail.c#34 (text+ko) ====

@@ -1199,6 +1199,11 @@
 		/* Allocate a new vnet if specified. */
 		pr->pr_vnet = (pr_flags & PR_VNET)
 		    ? vnet_alloc() : ppr->pr_vnet;
+		if (pr->pr_vnet == NULL) {
+			prison_deref(pr, PD_LIST_XLOCKED);
+			error = ENOMEM;
+			goto done_releroot;
+		}
 #endif
 		/*
 		 * Allocate a dedicated cpuset for each jail.
@@ -2456,7 +2461,7 @@
 		sx_downgrade(&allprison_lock);
 
 #ifdef VIMAGE
-		if (pr->pr_vnet != ppr->pr_vnet)
+		if (pr->pr_vnet != NULL && pr->pr_vnet != ppr->pr_vnet)
 			vnet_destroy(pr->pr_vnet);
 #endif
 		if (pr->pr_root != NULL) {

==== //depot/projects/vimage-commit2/src/sys/net/vnet.c#6 (text+ko) ====

@@ -216,6 +216,18 @@
 {
 	struct vnet *vnet;
 
+	/*
+	 * Do not proceed with a lengthy chain of direct and indirect
+	 * mallocs if kmem shortage can be anticipated.  This ad-hoc
+	 * check applies only to non-default vnets.
+	 */
+	if (vnet0 != NULL) {
+		vnet = malloc(1024*1024, M_VNET, M_NOWAIT | M_ZERO);
+		if (vnet == NULL)
+			return (NULL);
+		free(vnet, M_VNET);
+	}
+
 	vnet = malloc(sizeof(struct vnet), M_VNET, M_WAITOK | M_ZERO);
 	vnet->vnet_magic_n = VNET_MAGIC_N;