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Date: Tue, 12 Jun 2007 08:42:04 -0700
From: Sam Leffler <sam@errno.com>
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To: Jeff Roberson <jeff@FreeBSD.org>
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Cc: cvs-src@FreeBSD.org, src-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/sys proc.h src/sys/kern kern_thread.c
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Jeff Roberson wrote:
> jeff        2007-06-12 07:24:47 UTC
> 
>   FreeBSD src repository
> 
>   Modified files:
>     sys/sys              proc.h 
>     sys/kern             kern_thread.c 
>   Log:
>   Solve a complex exit race introduced with thread_lock:
>    - Add a count of exiting threads, p_exitthreads, to struct proc.
>    - Increment p_exithreads when we set the deadthread in thread_exit().
>    - When we thread_stash() a deadthread use an atomic to drop the count.
>    - Spin until the p_exithreads count reaches 0 in thread_wait().
>    - Lock the last exiting thread momentarily to be certain that it has
>      exited cpu_throw().
>    - Restructure thread_wait().  It does not need a loop as there will only
>      ever be one thread.

What are the symptoms of this race?  Since the sched lock changes I've 
repeatedly hit user-after-free crashes and other data corruption-like 
assert failures that appear to trigger through signals and exit.  These 
are all on UP (laptops).

	Sam