Re: closefrom blocking, wchan urdlck

> On 27 Dec 2021, at 16:19, Konstantin Belousov <kostikbel@gmail.com> wrote:
> 
> On Mon, Dec 27, 2021 at 04:13:50PM +0100, Jan Mikkelsen wrote:
>> 
>> 
>>> On 27 Dec 2021, at 16:03, Konstantin Belousov <kostikbel@gmail.com> wrote:
>>> 
>>> On Mon, Dec 27, 2021 at 03:54:57PM +0100, Jan Mikkelsen wrote:
>>>> 
>>>>> On 27 Dec 2021, at 14:52, Konstantin Belousov <kostikbel@gmail.com> wrote:
>>>>> 
>>>>> On Mon, Dec 27, 2021 at 01:39:11PM +0100, Jan Mikkelsen wrote:
>>>>>> Hi,
>>>>>> 
>>>>>> (On 11.2)
>>>>>> 
>>>>>> I am occasionally seeing closefrom() block in a child process created by a call to pdfork().
>>>>>> 
>>>>>> When this does happen, it is very early after the process has started, while other threads are being created elsewhere in the process. I cannot reproduce it after the thread creation is complete. According to the sigaction man page, this should be async signal safe.
>>>>>> 
>>>>>> Stack trace from the call to closefrom():
>>>>>> 
>>>>>> * frame #0: 0x000000080090276c libthr.so.3`_umtx_op_err at _umtx_op_err.S:37
>>>>>>  frame #1: 0x00000008008f6121 libthr.so.3`__thr_rwlock_rdlock(rwlock=<unavailable>, flags=<unavailable>, tsp=<unavailable>) at thr_umtx.c:307:10
>>>>>>  frame #2: 0x00000008008ff1ac libthr.so.3`_thr_rtld_rlock_acquire [inlined] _thr_rwlock_rdlock(rwlock=0x0000000800911600, flags=0, tsp=0x0000000000000000) at thr_umtx.h:232:10
>>>>>>  frame #3: 0x00000008008ff19b libthr.so.3`_thr_rtld_rlock_acquire(lock=0x0000000800911600) at thr_rtld.c:125
>>>>>>  frame #4: 0x000000080075332b ld-elf.so.1`rlock_acquire(lock=0x0000000800765270, lockstate=0x00007fffdfbfb8d0) at rtld_lock.c:208:2
>>>>>>  frame #5: 0x000000080074ba20 ld-elf.so.1`_rtld_bind(obj=0x0000000800769000, reloff=6072) at rtld.c:861:5
>>>>>>  frame #6: 0x0000000800747c7d ld-elf.so.1`_rtld_bind_start at rtld_start.S:121
>>>>>>  frame #7: 0x00000000006562d3 prog`Twio::ProcHandle::spawn(this=<unavailable>, command="/bin/echo", args=0x0000000800d7e000, descriptor_mapping=<unavailable>, descriptor_end=3) at prochandle_pdfork.cpp:308:2
>>>>> And where is the closefrom() call in the demonstrated trace?
>>>>> 
>>>>> What version of the system do you use?
>>>>> You need at least cbdec8db18b533f6d7be (on HEAD) or a5659943e37a74c96e
>>>>> (stable/13) for pdfork() to behave sanely.  But you still not allowed to
>>>>> call non-async signal safe functions in the child before exec.
>>>> 
>>>> 
>>>> This is 12.2-p11. I just noticed that I wrote 11.2 above, that is incorrect.
>> 
….

>>>> The commit you can apply cleanly to 12.2, I’m running a build now. Are there other issues with pdfork in 12.2?
>>> 
>>> pdfork() with threading processes requires 21f749da82e755aafab1276 and the
>>> followup cbdec8db18b533f6d7be.  I do not believe any of this is in 12.3,
>>> and definitely not in 12.2.
>> 
>> Thanks, will check and apply.

I can no longer reproduce the problem with these two changes added to a 12.2 source tree. Thanks!

Regards,

Jan M.