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From: John Baldwin <jhb@freebsd.org>
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Date: Thu, 31 Mar 2011 09:58:51 -0400
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	(bigwig.baldwin.cx); Thu, 31 Mar 2011 09:58:51 -0400 (EDT)
Cc: Svatopluk Kraus <onwahe@gmail.com>
Subject: Re: schedcpu() in /sys/kern/sched_4bsd.c calls thread_lock() on
	thread with un-initialized td_lock
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On Thursday, March 31, 2011 7:32:26 am Svatopluk Kraus wrote:
> Hi,
> 
>   I've got a page fault (because of NULL td_lock) in
> thread_lock_flags() called from schedcpu() in /sys/kern/sched_4bsd.c
> file. During process fork, new thread is linked to new process which
> is linked to allproc list and both allproc_lock and new process lock
> are unlocked before sched_fork() is called, where new thread td_lock
> is initialized. Only PRS_NEW process status is on sentry but not
> checked in schedcpu().

I think this should fix it:

Index: sched_4bsd.c
===================================================================
--- sched_4bsd.c	(revision 220190)
+++ sched_4bsd.c	(working copy)
@@ -463,6 +463,10 @@ schedcpu(void)
 	sx_slock(&allproc_lock);
 	FOREACH_PROC_IN_SYSTEM(p) {
 		PROC_LOCK(p);
+		if (p->p_state == PRS_NEW) {
+			PROC_UNLOCK(p);
+			continue;
+		}
 		FOREACH_THREAD_IN_PROC(p, td) {
 			awake = 0;
 			thread_lock(td);

-- 
John Baldwin