Re: [Emc-developers] EMC and RT-Preempt

[Michael A. <mic...@is...>]

Hello Lars,

Thanks for trying out...

On 06/19/2011 10:34 PM, Lars Segerlund wrote:
> command line ...
> root@smurf:/home/ls/src/emc/emc2-dev/src/hal# chrt 99 ./shm_interface_test
> Error while shmget
> Semaphore value is 0
> Waiting one second, then until semaphore gets released
> Segmenteringsfel
>
> dmesg ...
> [ 3579.723705] shm_interface_t[2462]: segfault at ffffffffa76ad000 ip
> 0000000000400d14 sp 00007fff128c4600 error 6 in
> shm_interface_test[400000+2000]
>
> I tried running with gdb but didn't get anything interesting, and it's
> not a lot.
>
> I tried strace also
>
> arch_prctl(ARCH_SET_FS, 0x7fcf1a3d9700) = 0
> mprotect(0x7fcf19b98000, 16384, PROT_READ) = 0
> mprotect(0x7fcf19da8000, 4096, PROT_READ) = 0
> mprotect(0x7fcf19fc0000, 4096, PROT_READ) = 0
> mprotect(0x7fcf1a3f8000, 4096, PROT_READ) = 0
> munmap(0x7fcf1a3dc000, 103274)          = 0
> set_tid_address(0x7fcf1a3d99d0)         = 2483
> set_robust_list(0x7fcf1a3d99e0, 0x18)   = 0
> futex(0x7fffd6bb89fc, FUTEX_WAKE_PRIVATE, 1) = 0
> futex(0x7fffd6bb89fc, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME,
> 1, NULL, 7fcf1a3d9700) = -1 EAGAIN (Resource temporarily unavailable)
> rt_sigaction(SIGRTMIN, {0x7fcf19daf860, [], SA_RESTORER|SA_SIGINFO,
> 0x7fcf19db8f60}, NULL, 8) = 0
> rt_sigaction(SIGRT_1, {0x7fcf19daf8f0, [],
> SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7fcf19db8f60}, NULL, 8) = 0
> rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
> getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
> shmget(0xcafe, 88, 0666)                = 2883607
> shmat(2883607, 0, 0)                    = ?
> statfs("/dev/shm", {f_type=0x1021994, f_bsize=4096, f_blocks=127182,
> f_bfree=127181, f_bavail=127181, f_files=127182, f_ffree=127179,
> f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
> futex(0x7fcf19fc52bc, FUTEX_WAKE_PRIVATE, 2147483647) = 0
> open("/dev/shm/sem.emcsem1", O_RDWR|O_NOFOLLOW) = 3
> fstat(3, {st_mode=S_IFREG|0755, st_size=32, ...}) = 0
> brk(0)                                  = 0xc9f000
> brk(0xcc0000)                           = 0xcc0000
> mmap(NULL, 32, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = 0x7fcf1a3f4000
> close(3)                                = 0
> fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
> mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
> 0) = 0x7fcf1a3f3000
> write(1, "Semaphore value is 0\n", 21Semaphore value is 0
> )  = 21
> write(1, "Waiting one second, then until s"..., 55Waiting one second,
> then until semaphore gets released
> ) = 55
> rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
> rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
> rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
> nanosleep({1, 0}, 0x7fffd6bb8860)       = 0
> --- SIGSEGV (Segmentation fault) @ 0 (0) ---
> +++ killed by SIGSEGV +++
> Segmenteringsfel
>
> And a small guess ... I'm running 64 bit ? ...

I don't know if 64 bit make problems in the EMC world. But I saw this in 
the output you sent: "Error while shmget". It seems like shmget fails 
for some reason, but the strace seems normal. And I saw that I forgot 
the exit statement in the error handler, this is probably the reason why 
it "Segmenteringsfels" later.

@@ -93,6 +93,7 @@ int main()
      id = shmget(key, size, SHM_PERMISSIONS);
      if (id == -1) {
           printf("Error while shmget\n");
+	 exit(-1);
          }

Can you maybe try to remove the two shm-memories with ipcrm?

>
> I have not had time to look to much at the code, since I have been ill
> this week, but It seems to run.
>   I have mostly been busy trying to get an USB driver running for my
> hardware, sorry but limited time.
>
>   I do believe that shm_interface_test ran a couple of times ....
>
>   Tell me if I can run any test, but at the moment I am actually more
> concearned about RT-Preempt EMC :-D ... which is a reason to be really
> happy.

Do you like to tell me what you intend to do with an RT_Preempted EMC? 
Doing this seems kind of "unusal"  :) .

>
>   Have you tried the mailinglist for rt-preempt about the timing ? it's
> on http://osadl.org/ , or lkml.org ... I knot the hpet timers have
> undergone some work.

Unfortunately, I had no time yet to look at the timing issues. It works 
quite well on some machines here, on some others there are few problems. 
Latencies around 100us are probably bad, but it's currently enough for 
our purposes.


Regards Michael

>
>   / regards, Lars Segerlund.
>
> 2011/6/19 Michael Abel<Mic...@is...>:
>>
>> Hi Lars,
>>
>> I walked a bit trough the code and tried some things out. There is already
>> cleanup code to avoid this problem, but the cleanup works only when emc is
>> started as root. It seems just like a problem with permissions. I recommend
>> to start emc as root to avoid the problems.
>>
>> In case of problems it's also possible to remove the shm by hand with these
>> commands:
>>
>> ipcrm -M 0x48414c32 #(hal shm)
>> ipcrm -M 0x0000cafe #(shm interface)
>>
>> Can you please tell me more about the segfaulting shm_tester? I have no
>> problems with this program here...
>> Thanks!
>>
>> regards Michael
>>

----------------------------------------------------------------
Dipl.-Ing. Michael Abel

Graduate School advanced Manufacturing Engineering
GSaME - Universität Stuttgart

Institut für Steuerungstechnik
der Werkzeugmaschinen und Fertigungseinrichtungen
ISW - Universität Stuttgart

Seidenstr. 36
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