From owner-freebsd-alpha  Sat Oct  7 13:33:30 2000
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From: Andrew Gallatin <gallatin@cs.duke.edu>
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Date: Sat,  7 Oct 2000 16:33:26 -0400 (EDT)
To: freebsd-alpha@freebsd.org
Cc: jhb@freebsd.org
Subject: kernacc in mtx_validate
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The calls to kerneacc in mtx_validate may fail when mtx_next points to
"all_mtx" because it is a k0seg address, it is not in mapped memory.
Because of this, anybody running with SMP_DEBUG & INVARIANTS will
notice this at boot:

panic: Assertion kernacc((caddr_t)all_mtx.mtx_next, 4, 1) == 1 failed at ../../alpha/alpha/synch_machdep.c:444
	and/or 
panic: mtx_validate: mp=0xfffffc000068a978 mp->mtx_next=0xfffffc000068a7a8


The following works around the problem by merrily accepting any k0seg
addr as possibly valid:

Index: alpha/alpha/synch_machdep.c
===================================================================
RCS file: /home/ncvs/src/sys/alpha/alpha/synch_machdep.c,v
retrieving revision 1.5
diff -u -r1.5 synch_machdep.c
--- alpha/alpha/synch_machdep.c	2000/10/04 01:20:49	1.5
+++ alpha/alpha/synch_machdep.c	2000/10/07 20:21:03
@@ -428,6 +428,9 @@
 
 #ifdef SMP_DEBUG
 
+#define ISK0SEG(va)	\
+	((va >= ALPHA_K0SEG_BASE && va <= ALPHA_K0SEG_END))
+
 int mtx_validate __P((struct mtx *, int));
 
 int
@@ -441,10 +444,12 @@
 		return 0;
 
 	mtx_enter(&all_mtx, MTX_DEF);
-	ASS(kernacc((caddr_t)all_mtx.mtx_next, 4, 1) == 1);
+	ASS(ISK0SEG((vm_offset_t)all_mtx.mtx_next) || 
+	    kernacc((caddr_t)all_mtx.mtx_next, 4, 1) == 1); 
 	ASS(all_mtx.mtx_next->mtx_prev == &all_mtx);
 	for (i = 0, mp = all_mtx.mtx_next; mp != &all_mtx; mp = mp->mtx_next) {
-		if (kernacc((caddr_t)mp->mtx_next, 4, 1) != 1) {
+		if (!ISK0SEG((vm_offset_t)all_mtx.mtx_next) &&
+		    kernacc((caddr_t)mp->mtx_next, 4, 1) != 1) {
 			panic("mtx_validate: mp=%p mp->mtx_next=%p",
 			    mp, mp->mtx_next);
 		}


Comments?

Drew

------------------------------------------------------------------------------
Andrew Gallatin, Sr Systems Programmer	http://www.cs.duke.edu/~gallatin
Duke University				Email: gallatin@cs.duke.edu
Department of Computer Science		Phone: (919) 660-6590


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