[Vm-dev] Problem with OSSubprocess / signals / heartbeat ?

Tue Dec 20 09:30:41 UTC 2016

Hi Holger,

Just to add to the issue, when we talk about hanging, the VM thread is 
stopped in an FFI call,

0xffdfe1c0 I 
OSSUnixSubprocess>primitivePosixSpawn:command:fileActions:attributes:argPointer:envPointer: 
0x9482438: a(n) OSSUnixSubprocess
0xffdfe200 I OSSUnixSubprocess>internalRun 0x9482438: a(n) OSSUnixSubprocess
0xffdfe220 I [] in OSSUnixSubprocess>run 0x9482438: a(n) OSSUnixSubprocess
0xffdf9fe0 M BlockClosure>ensure: 0x9482750: a(n) BlockClosure
0xffdfa004 I OSSUnixSubprocess>run 0x9482438: a(n) OSSUnixSubprocess
0xffdfa024 I OSSUnixSubprocess>runAndWaitOnExitDo: 0x9482438: a(n) 
OSSUnixSubprocess

self ffiCall: #( int posix_spawnp (void* pidPointer, String 
commandString, void* fileActions, void * attributes, void* argPointer, 
void* envPointer) )

Now, here is an extract of the timestamped `strace -ftt` of the hanging 
process:

[pid 24108] 10:28:09.044534 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.044577 gettimeofday({1482226089, 44582}, NULL) = 0
[pid 24108] 10:28:09.044644 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.044664 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.050924 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.050970 gettimeofday({1482226089, 50976}, NULL) = 0
[pid 24108] 10:28:09.050996 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.051009 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.051016 gettimeofday({1482226089, 51020}, NULL) = 0
[pid 24108] 10:28:09.051028 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.051040 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.066154 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.066196 gettimeofday({1482226089, 66201}, NULL) = 0
[pid 24108] 10:28:09.066220 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.066233 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.072599 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.072643 gettimeofday({1482226089, 72648}, NULL) = 0
[pid 24108] 10:28:09.072716 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.072740 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.079552 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.079580 gettimeofday({1482226089, 79585}, NULL) = 0
[pid 24108] 10:28:09.079648 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.079672 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.089178 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.089233 gettimeofday({1482226089, 89239}, NULL) = 0
[pid 24108] 10:28:09.089264 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.089278 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.101007 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.101046 gettimeofday({1482226089, 101050}, NULL) = 0
[pid 24108] 10:28:09.101096 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.101116 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.107650 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.107699 gettimeofday({1482226089, 107706}, NULL) = 0
[pid 24108] 10:28:09.107771 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.107789 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.116188 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---
[pid 24108] 10:28:09.116226 gettimeofday({1482226089, 116232}, NULL) = 0
[pid 24108] 10:28:09.116254 sigreturn() (mask []) = 120
[pid 24108] 10:28:09.116273 clone(child_stack=0, 
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xf7500768) = ? ERESTARTNOINTR (To be restarted)
[pid 24108] 10:28:09.129739 --- SIGALRM {si_signo=SIGALRM, 
si_code=SI_KERNEL} ---

The second trace in Mariano's email was a trace in the case of no FFI 
call. Just to compare both of them and their differences, but there is 
no hang in there.
Although my knowledge arrives until here, I can help in providing any 
other traces or information.

I asked Santa an OSSubprocess that won't hang :)

Thanks,
Guille

-------- Original Message --------
>   
>
>> On 19 Dec 2016, at 14:41, Mariano Martinez Peck <marianopeck at gmail.com> wrote:
>>
>> Hi guys,
>>
>> Guille Polito kept one of these images if someone can give us a hand. He also proposed the great idea of using `strace` to see what was going on. He  (together with Pable Tesone) suspected that the heartbeat could be interrupting the `clone()` function which is (I think) called internally by the 'posix_spawn()' which is the one used by OSSubprocess.
>>
>> When these images are "hung" they found at a infinitive loop like this:
> Okay, how many child processes do you have at that point? How many processes does the system have?
>
>
>> [pid 17477] --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
>> [pid 17477] gettimeofday({1482152630, 593498}, NULL) = 0
>> [pid 17477] sigreturn() (mask [])       = 120
>> [pid 17477] clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xf7578768) = ? ERESTARTNOINTR (To be restarted)
>> [pid 17477] --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
>> [pid 17477] gettimeofday({1482152630, 600126}, NULL) = 0
>> [pid 17477] sigreturn() (mask [])       = 120
>> [pid 17477] clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0xf7578768) = ? ERESTARTNOINTR (To be restarted)
> so above.. 7ms between the two gettimeofday calls? Nothing else? Set a breakpoint on clone/fork in gdb and look at the c-stack at this point? Could you strace with timestamps to see how much time is spent? Is the process suspicious in other ways?
>
> So yes.. sounds like clone doesn't complete.. the question is why? Is it out of resources? Is something in the VM blocking longer than the heartbeat, is the heartbeat more frequent than expected?
>
>
>> As you can see, there is a SIGALARM involved. It also looks like the `gettimeofday` is used by the heartbeat ?  Could it be that someone the heartbeat is interrupting the `clone()` ?
>>
>> Guille also showed me the `strace` output with a regular / working image:
>>
>>
>> [pid 18647] --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
>> [pid 18647] gettimeofday({1482152829, 481014}, NULL) = 0
>> [pid 18647] sigreturn() (mask [])       = -1 EINTR (Interrupted system call)
>> [pid 18647] getitimer(ITIMER_REAL, {it_interval={0, 2000}, it_value={0, 1917}}) = 0
>> [pid 18647] recvmsg(3, 0xff7b0734, 0)   = -1 EAGAIN (Resource temporarily unavailable)
>> [pid 18647] select(4, [3], [], [3], {0, 1000}) = 0 (Timeout)
>> [pid 18647] getitimer(ITIMER_REAL, {it_interval={0, 2000}, it_value={0, 797}}) = 0
>> [pid 18647] recvmsg(3, 0xff7b0734, 0)   = -1 EAGAIN (Resource temporarily unavailable)
>> [pid 18647] select(4, [3], [], [3], {0, 1000}) = ? ERESTARTNOHAND (To be restarted if no handler)
>> [pid 18647] --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
>>
>>
>> Does anyone have any hint here?
> Get timestamps in there. How long does it take to fail/end in this situation?
>
> holger
>
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