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References: <jejrbe$or8$1@dough.gmane.org> <201201110806.30620.jhb@freebsd.org>
From: Ivan Voras <ivoras@freebsd.org>
Date: Wed, 11 Jan 2012 15:33:30 +0100
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Cc: freebsd-hackers@freebsd.org, davidxu@freebsd.org
Subject: Re: sem(4) lockup in python?
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On 11 January 2012 14:06, John Baldwin <jhb@freebsd.org> wrote:
> 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
>> =C2=A0 =C2=A0PID =C2=A0 =C2=A0TID COMM =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 TDNAME =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 KSTACK
>>
>> 19008 101605 python =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 - =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0mi_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. =C2=
=A0He is
> probably the best person to ask (cc'd).
>

Ok, I've encountered the problem repeatedly while building databases/tdb:
 it uses Python in the build process (but maybe it needs something else in
parallel to provoke the problem).