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From: John Baldwin <jhb@freebsd.org>
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	(bigwig.baldwin.cx); Wed, 11 Jan 2012 08:06:34 -0500 (EST)
Cc: Ivan Voras <ivoras@freebsd.org>, davidxu@freebsd.org
Subject: Re: sem(4) lockup in python?
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On Wednesday, January 11, 2012 6:21:18 am Ivan Voras wrote:
> The lang/python27 port can optionally be built with the support for 
> POSIX semaphores - i.e. sem(4). This option is labeled as experimental 
> so it may be that the code is simply incorrect. I've tried it and get 
> frequent hangs with the python process in the "usem" state. The kernel 
> stack is as follows and looks reasonable:
> 
> # procstat -kk 19008
>    PID    TID COMM             TDNAME           KSTACK 
> 
> 19008 101605 python           -                mi_switch+0x174 
> sleepq_catch_signals+0x2f4 sleepq_wait_sig+0x16 _sleep+0x269 
> do_sem_wait+0xa19 __umtx_op_sem_wait+0x51 amd64_syscall+0x450 
> Xfast_syscall+0xf7
> 
> The process doesn't react to SIGINT or SIGTERM but fortunately reacts to 
> SIGKILL.
> 
> This could be an error in Python code but OTOH this code is not 
> FreeBSD-specific so it's unlikely.

This is using the new umtx-based semaphore code that David Xu wrote.  He is
probably the best person to ask (cc'd).

-- 
John Baldwin