[erlang-bugs] VM locks up on write to socket (and now it seems to file too)

Patrik Nyblom <>
Wed Nov 28 16:54:47 CET 2012


Hi!

I'll upgrade the CentOS VM I have to 6.3 (only had 6.1 :() and see if I 
can reproduce. If that fails, could you run a VM with a patch to try to 
handle the unexpected case and see if that fixes it?

Cheers,
/Patrik
On 11/24/2012 02:57 PM, Peter Membrey wrote:
> Hi guys,
>
> Thanks for getting back in touch so quickly!
>
> I did do an lsof on the process and I can confirm that it was
> definitely a socket. However by that time the application it had been
> trying to send to had been killed. When I checked the sockets were
> showing as waiting to close. Unfortunately I didn't think to do an
> lsof until after the apps had been shut down. I was hoping the VM
> would recover if I killed the app that had upset it. However even
> after all the apps connected had been shut down, the issue didn't
> resolve.
>
> The application receives requests from a client, which contains two
> data items. The stream ID and a timestamp. Both are encoded as big
> integer unsigned numbers. The server then looks through the file
> referenced by the stream ID and uses the timestamp as an index. The
> file format is currently really simple, in the form of:
>
> <Timestamp:64/native-integer,Length:32/native-integer,Data:Length/binary>>
>
> There is an index file that provides an offset into the file based on
> time stamp, but basically it opens the file, and reads sequentially
> through it until it finds the timestamps that it cares about. In this
> case it reads all data with a greater timestamp until the end of the
> file is reached. It's possible the client is sending an incorrect
> timestamp, and maybe too much data is being read. However the loop is
> very primitive - it reads all the data in one go before passing it
> back to the protocol handler to send down the socket; so by that time
> even though the response is technically incorrect and the app has
> failed, it should still not cause the VM any issues.
>
> The data is polled every 10 seconds by the client app so I would not
> expect there to be 2GB of new data to send. I'm afraid my C skills are
> somewhat limited, so I'm not sure how to put together a sample app to
> try out writev. The platform is 64bit CentOS 6.3 (equivalent to RHEL
> 6.3) so I'm not expecting any strange or weird behaviour from the OS
> level but of course I could be completely wrong there. The OS is
> running directly on hardware, so there's no VM layer to worry about.
>
> Hope this might offer some additional clues…
>
> Thanks again!
>
> Kind Regards,
>
> Peter Membrey
>
>
>
> On 24 November 2012 00:13, Patrik Nyblom <> wrote:
>> Hi again!
>>
>> Could you go back to the version without the printouts and get back to the
>> situation where writev loops returning 0 (as in the strace)? If so, it would
>> be really interesting to see an 'lsof' of the beam process, to see if this
>> file descriptor really is open and is a socket...
>>
>> The thing is that writev with a vector that is not empty, would never return
>> 0 for a non blocking socket. Not on any modern (i.e. not ancient) POSIX
>> compliant system anyway. Of course it is a *really* large item you are
>> trying to write there, but it should be no problem for a 64bit linux.
>>
>> Also I think there is no use finding the Erlang code, I'll take that back,
>> It would be more interesting to see what really happens at the OS/VM level
>> in this case.
>>
>> Cheers,
>> Patrik
>>
>>
>> On 11/23/2012 01:49 AM, Loïc Hoguin wrote:
>>> Sending this on behalf of someone who didn't manage to get the email sent
>>> to this list after 2 attempts. If someone can check if he's hold up or
>>> something that'd be great.
>>>
>>> Anyway he has a big issue so I hope I can relay the conversation reliably.
>>>
>>> Thanks!
>>>
>>> On 11/23/2012 01:45 AM, Peter Membrey wrote:
>>>> From: Peter Membrey <>
>>>> Date: 22 November 2012 19:02
>>>> Subject: VM locks up on write to socket (and now it seems to file too)
>>>> To: 
>>>>
>>>>
>>>> Hi guys,
>>>>
>>>> I wrote a simple database application called CakeDB
>>>> (https://github.com/pmembrey/cakedb) that basically spends its time
>>>> reading and writing files and sockets. There's very little in the way
>>>> of complex logic. It is running on CentOS 6.3 with all the updates
>>>> applied. I hit this problem on R15B02 so I rolled back to R15B01 but
>>>> the issue remained. Erlang was built from source.
>>>>
>>>> The machine has two Intel X5690 CPUs giving 12 cores plus HT. I've
>>>> tried various arguments for the VM but so far nothing has prevented
>>>> the problem. At the moment I'm using:
>>>>
>>>> +K
>>>> +A 6
>>>> +sbt tnnps
>>>>
>>>> The issue I'm seeing is that one of the scheduler threads will hit
>>>> 100% cpu usage and the entire VM will become unresponsive. When this
>>>> happens, I am not able to connect via the console with attach and
>>>> entop is also unable to connect. I can still establish TCP connections
>>>> to the application, but I never receive a response. A standard kill
>>>> signal will cause the VM to shut down (it doesn't need -9).
>>>>
>>>> Due to the pedigree of the VM I am quite willing to accept that I've
>>>> made a fundamental mistake in my code. I am pretty sure that the way I
>>>> am doing the file IO could result in some race conditions. However, my
>>>> poor code aside, from what I understand, I still shouldn't be able to
>>>> crash / deadlock the VM like this.
>>>>
>>>> The issue doesn't seem to be caused by load. The app can fail when
>>>> it's very busy, but also when it is practically idle. I haven't been
>>>> able to find a trigger or any other explanation for the failure.
>>>>
>>>> The thread maxing out the CPU is attempting to write data to the socket:
>>>>
>>>> (gdb) bt
>>>> #0  0x00007f9882ab6377 in writev () from /lib64/libc.so.6
>>>> #1  0x000000000058a81f in tcp_inet_output (data=0x2407570,
>>>> event=<value optimized out>) at drivers/common/inet_drv.c:9681
>>>> #2  tcp_inet_drv_output (data=0x2407570, event=<value optimized out>)
>>>> at drivers/common/inet_drv.c:9601
>>>> #3  0x00000000004b773f in erts_port_task_execute (runq=0x7f98826019c0,
>>>> curr_port_pp=0x7f9881639338)  at beam/erl_port_task.c:858
>>>> #4  0x00000000004afd83 in schedule (p=<value optimized out>,
>>>> calls=<value optimized out>) at beam/erl_process.c:6533
>>>> #5  0x0000000000539ca2 in process_main () at beam/beam_emu.c:1268
>>>> #6  0x00000000004b1279 in sched_thread_func (vesdp=0x7f9881639280) at
>>>> beam/erl_process.c:4834
>>>> #7  0x00000000005ba726 in thr_wrapper (vtwd=0x7fff6cfe2300) at
>>>> pthread/ethread.c:106
>>>> #8  0x00007f9882f78851 in start_thread () from /lib64/libpthread.so.0
>>>> #9  0x00007f9882abe11d in clone () from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>> I then tried running strace on that thread and got (indefinitely):
>>>>
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> writev(15, [{"", 2158022464}], 1)       = 0
>>>> ...
>>>>
>>>>   From what I can tell, it's trying to write data to a socket, which is
>>>> succeeding, but writing 0 bytes. From the earlier definitions in the
>>>> source file, an error condition would be signified by a negative
>>>> number. Any other result is the number of bytes written, in this case
>>>> 0. I'm not sure if this is desired behaviour or not. I've tried
>>>> killing the application on the other end of the socket, but it has no
>>>> effect on the VM.
>>>>
>>>> I have enabled debugging for the inet code, so hopefully this will
>>>> give a little more insight. I am currently trying to reproduce the
>>>> condition, but as I really have no idea what causes it, it's pretty
>>>> much a case of wait and see.
>>>>
>>>>
>>>> **** UPDATE ****
>>>>
>>>> I managed to lock up the VM again, but this time it was caused by file
>>>> IO,
>>>> probably from the debugging statements. Although it worked fine for some
>>>> time
>>>> the last entry in the file was cut off.
>>>>
>>>>   From GDB:
>>>>
>>>> (gdb) info threads
>>>>     53 Thread 0x7f83e988b700 (LWP 8621)  0x00007f83ea6da54d in read ()
>>>> from /lib64/libpthread.so.0
>>>>     52 Thread 0x7f83e8c8f700 (LWP 8622)  0x00007f83ea6d743c in
>>>> pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
>>>>     51 Thread 0x7f83e818d700 (LWP 8623)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     50 Thread 0x7f83e816b700 (LWP 8624)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     49 Thread 0x7f83e8149700 (LWP 8625)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     48 Thread 0x7f83e8127700 (LWP 8626)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     47 Thread 0x7f83e8105700 (LWP 8627)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     46 Thread 0x7f83e80e3700 (LWP 8628)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     45 Thread 0x7f83e80c1700 (LWP 8629)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     44 Thread 0x7f83e809f700 (LWP 8630)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     43 Thread 0x7f83e807d700 (LWP 8631)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     42 Thread 0x7f83e805b700 (LWP 8632)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     41 Thread 0x7f83e8039700 (LWP 8633)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     40 Thread 0x7f83e8017700 (LWP 8634)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     39 Thread 0x7f83e7ff5700 (LWP 8635)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     38 Thread 0x7f83e7fd3700 (LWP 8636)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     37 Thread 0x7f83e7fb1700 (LWP 8637)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     36 Thread 0x7f83e7f8f700 (LWP 8638)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     35 Thread 0x7f83e7f6d700 (LWP 8639)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     34 Thread 0x7f83e7f4b700 (LWP 8640)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     33 Thread 0x7f83e7f29700 (LWP 8641)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     32 Thread 0x7f83e7f07700 (LWP 8642)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     31 Thread 0x7f83e7ee5700 (LWP 8643)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     30 Thread 0x7f83e7ec3700 (LWP 8644)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     29 Thread 0x7f83e7ea1700 (LWP 8645)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     28 Thread 0x7f83e7e7f700 (LWP 8646)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     27 Thread 0x7f83d7c5a700 (LWP 8647)  0x00007f83ea6db09d in waitpid
>>>> () from /lib64/libpthread.so.0
>>>>     26 Thread 0x7f83d7c53700 (LWP 8648)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     25 Thread 0x7f83d7252700 (LWP 8649)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     24 Thread 0x7f83d6851700 (LWP 8650)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     23 Thread 0x7f83d5e50700 (LWP 8651)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     22 Thread 0x7f83d544f700 (LWP 8652)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     21 Thread 0x7f83d4a4e700 (LWP 8653)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     20 Thread 0x7f83d404d700 (LWP 8654)  0x00007f83ea20be7d in write ()
>>>> from /lib64/libc.so.6
>>>>     19 Thread 0x7f83d364c700 (LWP 8655)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     18 Thread 0x7f83d2c4b700 (LWP 8656)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     17 Thread 0x7f83d224a700 (LWP 8657)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     16 Thread 0x7f83d1849700 (LWP 8658)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     15 Thread 0x7f83d0e48700 (LWP 8659)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     14 Thread 0x7f83d0447700 (LWP 8660)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     13 Thread 0x7f83cfa46700 (LWP 8661)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     12 Thread 0x7f83cf045700 (LWP 8662)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     11 Thread 0x7f83ce644700 (LWP 8663)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     10 Thread 0x7f83cdc43700 (LWP 8664)  0x00007f83ea215ae9 in syscall
>>>> () from /lib64/libc.so.6
>>>>     9 Thread 0x7f83cd242700 (LWP 8665)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     8 Thread 0x7f83cc841700 (LWP 8666)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     7 Thread 0x7f83cbe40700 (LWP 8667)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     6 Thread 0x7f83cb43f700 (LWP 8668)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     5 Thread 0x7f83caa3e700 (LWP 8669)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     4 Thread 0x7f83ca03d700 (LWP 8670)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     3 Thread 0x7f83c963c700 (LWP 8671)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>>     2 Thread 0x7f83c8c3b700 (LWP 8672)  0x00007f83ea215ae9 in syscall ()
>>>> from /lib64/libc.so.6
>>>> * 1 Thread 0x7f83eb3a8700 (LWP 8597)  0x00007f83ea211d03 in select ()
>>>> from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>>
>>>> (gdb) bt
>>>> #0  0x00007f83ea20be7d in write () from /lib64/libc.so.6
>>>> #1  0x00007f83ea1a2583 in _IO_new_file_write () from /lib64/libc.so.6
>>>> #2  0x00007f83ea1a3b35 in _IO_new_do_write () from /lib64/libc.so.6
>>>> #3  0x00007f83ea1a21fd in _IO_new_file_xsputn () from /lib64/libc.so.6
>>>> #4  0x00007f83ea17589d in vfprintf () from /lib64/libc.so.6
>>>> #5  0x00007f83ea18003a in printf () from /lib64/libc.so.6
>>>> #6  0x000000000058f0e8 in tcp_recv (desc=0x2c3d350, request_len=0) at
>>>> drivers/common/inet_drv.c:8976
>>>> #7  0x000000000058f63a in tcp_inet_input (data=0x2c3d350, event=<value
>>>> optimized out>) at drivers/common/inet_drv.c:9326
>>>> #8  tcp_inet_drv_input (data=0x2c3d350, event=<value optimized out>)
>>>> at drivers/common/inet_drv.c:9604
>>>> #9  0x00000000004b770f in erts_port_task_execute (runq=0x7f83e9d5d3c0,
>>>> curr_port_pp=0x7f83e8dc6e78) at beam/erl_port_task.c:851
>>>> #10 0x00000000004afd83 in schedule (p=<value optimized out>,
>>>> calls=<value optimized out>) at beam/erl_process.c:6533
>>>> #11 0x0000000000539ca2 in process_main () at beam/beam_emu.c:1268
>>>> #12 0x00000000004b1279 in sched_thread_func (vesdp=0x7f83e8dc6dc0) at
>>>> beam/erl_process.c:4834
>>>> #13 0x00000000005bb3e6 in thr_wrapper (vtwd=0x7fffe8266da0) at
>>>> pthread/ethread.c:106
>>>> #14 0x00007f83ea6d3851 in start_thread () from /lib64/libpthread.so.0
>>>> #15 0x00007f83ea21911d in clone () from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>> (gdb) bt
>>>> #0  0x00007f83ea6da54d in read () from /lib64/libpthread.so.0
>>>> #1  0x0000000000554b6e in signal_dispatcher_thread_func (unused=<value
>>>> optimized out>) at sys/unix/sys.c:2776
>>>> #2  0x00000000005bb3e6 in thr_wrapper (vtwd=0x7fffe8266c80) at
>>>> pthread/ethread.c:106
>>>> #3  0x00007f83ea6d3851 in start_thread () from /lib64/libpthread.so.0
>>>> #4  0x00007f83ea21911d in clone () from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>> (gdb) bt
>>>> #0  0x00007f83ea215ae9 in syscall () from /lib64/libc.so.6
>>>> #1  0x00000000005bba35 in wait__ (e=0x2989390) at
>>>> pthread/ethr_event.c:92
>>>> #2  ethr_event_wait (e=0x2989390) at pthread/ethr_event.c:218
>>>> #3  0x00000000004ae5bd in erts_tse_wait (fcalls=<value optimized out>,
>>>> esdp=0x7f83e8e2c440, rq=0x7f83e9d5e7c0) at beam/erl_threads.h:2319
>>>> #4  scheduler_wait (fcalls=<value optimized out>, esdp=0x7f83e8e2c440,
>>>> rq=0x7f83e9d5e7c0) at beam/erl_process.c:2087
>>>> #5  0x00000000004afb94 in schedule (p=<value optimized out>,
>>>> calls=<value optimized out>) at beam/erl_process.c:6467
>>>> #6  0x0000000000539ca2 in process_main () at beam/beam_emu.c:1268
>>>> #7  0x00000000004b1279 in sched_thread_func (vesdp=0x7f83e8e2c440) at
>>>> beam/erl_process.c:4834
>>>> #8  0x00000000005bb3e6 in thr_wrapper (vtwd=0x7fffe8266da0) at
>>>> pthread/ethread.c:106
>>>> #9  0x00007f83ea6d3851 in start_thread () from /lib64/libpthread.so.0
>>>> #10 0x00007f83ea21911d in clone () from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>>
>>>> (gdb) bt
>>>> #0  0x00007f83ea6db09d in waitpid () from /lib64/libpthread.so.0
>>>> #1  0x0000000000555a9f in child_waiter (unused=<value optimized out>)
>>>> at sys/unix/sys.c:2700
>>>> #2  0x00000000005bb3e6 in thr_wrapper (vtwd=0x7fffe8266d50) at
>>>> pthread/ethread.c:106
>>>> #3  0x00007f83ea6d3851 in start_thread () from /lib64/libpthread.so.0
>>>> #4  0x00007f83ea21911d in clone () from /lib64/libc.so.6
>>>> (gdb)
>>>>
>>>>
>>>> **** END UPDATE ****
>>>>
>>>>
>>>> I'm happy to provide any information I can, so please don't hesitate to
>>>> ask.
>>>>
>>>> Thanks in advance!
>>>>
>>>> Kind Regards,
>>>>
>>>> Peter Membrey
>>>>
>>>
>> _______________________________________________
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>> 
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