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Would it be possible to change proc0_init() to initialize vmspace0 and
proc0->p_vmspace before anything else?

I recently stumbled upon a MUTEX_ACQUIRE() bug on VAX, which caused a
page fault in proc0_init() before this initialization took place. This
caused the page fault handler to dereference a NULL pointer and fault
again, which recursed until a "kernel stack invalid" panic happened.

Doing this initialization early in proc0_init() makes this page fault
cause a "Segv in kernel mode" panic which shows the real problem and
which I would have expected in first place.


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%SYSTEM-F-ANARCHISM, The operating system has been overthrown

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Index: sys/kern/kern_proc.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_proc.c,v
retrieving revision 1.106
diff -u -r1.106 kern_proc.c
--- sys/kern/kern_proc.c	4 Mar 2007 06:03:05 -0000	1.106
+++ sys/kern/kern_proc.c	9 Mar 2007 23:42:47 -0000
@@ -301,6 +301,15 @@
 	sess = &session0;
 	l = &lwp0;
 
+	/*
+	 * Initialize proc0's vmspace, which uses the kernel pmap.
+	 * All kernel processes (which never have user space mappings)
+	 * share proc0's vmspace, and thus, the kernel pmap.
+	 */
+	uvmspace_init(&vmspace0, pmap_kernel(), round_page(VM_MIN_ADDRESS),
+	    trunc_page(VM_MAX_ADDRESS));
+	p->p_vmspace = &vmspace0;
+
 	/* XXX p_smutex can be IPL_VM except for audio drivers */
 	mutex_init(&p->p_smutex, MUTEX_SPIN, IPL_SCHED);
 	mutex_init(&p->p_stmutex, MUTEX_SPIN, IPL_STATCLOCK);
@@ -401,15 +410,6 @@
 	/* Initialize file descriptor table for proc0. */
 	p->p_fd = &filedesc0.fd_fd;
 	fdinit1(&filedesc0);
-
-	/*
-	 * Initialize proc0's vmspace, which uses the kernel pmap.
-	 * All kernel processes (which never have user space mappings)
-	 * share proc0's vmspace, and thus, the kernel pmap.
-	 */
-	uvmspace_init(&vmspace0, pmap_kernel(), round_page(VM_MIN_ADDRESS),
-	    trunc_page(VM_MAX_ADDRESS));
-	p->p_vmspace = &vmspace0;
 
 	l->l_addr = proc0paddr;				/* XXX */
 

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