cvs commit: src/sys/sys proc.h src/sys/kern kern_thread.c

[Sam Leffler]

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