From owner-freebsd-smp  Thu Sep 28 17:18:49 2000
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To: sgk@troutmask.apl.washington.edu
Cc: freebsd-smp@FreeBSD.ORG
Subject: Re: 2 panics with MP kernels
From: Tor.Egge@fast.no
In-Reply-To: Your message of "Thu, 28 Sep 2000 13:17:25 -0700 (PDT)"
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> Again, I haven't been able to convince the system to
> produce a crash dump.

Currently, recursive panics on SMP machines causes infinite recursion
due to s_lock calling panic if the lock is already held by the same CPU.
The "panic" command on the ddb prompt only results in a "Fatal double fault".

The enclosed patch might help.

- Tor Egge


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Index: kern_shutdown.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/kern_shutdown.c,v
retrieving revision 1.83
diff -u -r1.83 kern_shutdown.c
--- kern_shutdown.c	2000/09/17 12:20:49	1.83
+++ kern_shutdown.c	2000/09/25 12:19:16
@@ -67,6 +67,7 @@
 #include <machine/md_var.h>
 #include <machine/mutex.h>
 #include <machine/smp.h>		/* smp_active, cpuid */
+#include <machine/globaldata.h>
 
 #include <sys/signalvar.h>
 
@@ -541,6 +542,10 @@
 
 #ifdef SMP
 	/* Only 1 CPU can panic at a time */
+#ifdef __i386__
+	/* Avoid fatal double fault */
+	if (panic_lock.lock_data != GLOBALDATA->gd_cpu_lockid) 
+#endif
 	s_lock(&panic_lock);
 #endif
 

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