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

Patrik Nyblom <>
Fri Nov 23 17:13:17 CET 2012


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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