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Date: Thu, 8 Jan 1998 04:26:52 GMT
From: Luoqi Chen <luoqi@luoqi.watermarkgroup.com>
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To: FreeBSD-gnats-submit@FreeBSD.ORG
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Subject: kern/5458: page fault during proc0 init & fix
Sender: owner-freebsd-bugs@FreeBSD.ORG
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>Number:         5458
>Category:       kern
>Synopsis:       page fault in proc0_init() & fix
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu Jan  8 14:33:17 PST 1998
>Last-Modified:
>Originator:     Luoqi Chen
>Organization:
The Watermark Group
>Release:        FreeBSD 3.0-CURRENT i386
>Environment:

	UP kernel cvsupped as of 1/7/1998

>Description:

	When pmap_pinit0() allocates a page for proc0's page
	directory, kernal page table may need to be extended.
	But while growing the kernel page table (pmap_growkernel()),
	newly allocated kernel page table pages are entered into
	every process' page directory. For proc0, the page
	directory is not allocated yet, and results in a page fault.
	Eventually, the machine panics with "lockmgr: not holding
	exclusive lock".

>How-To-Repeat:

	Not sure.

>Fix:
	
	In init_main.c:proc0_init(), move the call to pmap_pinit0()
	two lines up, right before proc0->p_vmspace is set. Because
	vmspace is not set, proc0 will be skipped when growing
	kernel page table.

Index: init_main.c
===================================================================
RCS file: /fun/cvs/src/sys/kern/init_main.c,v
retrieving revision 1.79
diff -u -r1.79 init_main.c
--- init_main.c	1997/12/14 02:10:12	1.79
+++ init_main.c	1998/01/08 07:14:29
@@ -399,9 +399,9 @@
 	limit0.p_refcnt = 1;
 
 	/* Allocate a prototype map so we have something to fork. */
+	pmap_pinit0(&vmspace0.vm_pmap);
 	p->p_vmspace = &vmspace0;
 	vmspace0.vm_refcnt = 1;
-	pmap_pinit0(&vmspace0.vm_pmap);
 	vm_map_init(&vmspace0.vm_map, round_page(VM_MIN_ADDRESS),
 	    trunc_page(VM_MAXUSER_ADDRESS), TRUE);
 	vmspace0.vm_map.pmap = &vmspace0.vm_pmap;
>Audit-Trail:
>Unformatted: