[Xenomai-help] rt_task_join() call hangs in shared lib destructor

[Mauro Salvini <mauro.salvini@domain.hid>]

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Hi, 

as from mail subject, I have an issue with rt_task_join() when called into shared object destructor.

I run xenomai 2.5.5.2 IPipe patch 2.7-4 on x86 2.6.35.7 kernel, Ubuntu Lucid 10.04.1. 
I have a simple code attached to mail, where main program opens a shared object with dlopen(). Shared object constructor launches a joinable real-time task. Main program sleeps 5 seconds and then calls dlclose(). Shared object destructor breaks real time task cycle and joins task, but rt_join_call() hangs application indefinitely. 

Initially it seems me to be due to this libc bug: 
https://bugzilla.redhat.com/show_bug.cgi?id=549813 

In facts my system originally has libc6 version 2.11.1 that contains this bug (attached example to bugtrace hangs on pthread_join() call). 
So I patched libc with suggested patch (that was applied on libc6 2.12, but unfortunately I cannot install it from .deb package because it was built for Ubuntu 10.10 only). Then I rebuild deb package with debuild command and updated my libc6 library: pthread_join() issue disappears, but rt_task_join() issue stills remain. 

I tried to run same xenomai-patched kernel on an Ubuntu 10.10 system (that comes with libc6 version 2.12), same result obtained (rt_task_join() hangs). 

I run test application under gdb, this is the backtrace for each task when it hangs: 

(gdb) info thread
  3 Thread 0xb7e34b70 (LWP 1684)  0xb7fe2424 in __kernel_vsyscall ()
  2 Thread 0xb7e42b70 (LWP 1683)  0xb7fe2424 in __kernel_vsyscall ()
* 1 Thread 0xb7e436d0 (LWP 1680)  0xb7fe2424 in __kernel_vsyscall ()


thread 1: 
(gdb) bt
#0  0xb7fe2424 in __kernel_vsyscall ()
#1  0xb7fb7b5d in pthread_join () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb7fd7181 in rt_task_join () from /usr/xenomai/lib/libnative.so.3
#3  0xb7e357ad in TestModExit () at TestMod.c:35
#4  0xb7e35668 in __do_global_dtors_aux () from ./libTestMod.so
#5  0xb7e35820 in _fini () from ./libTestMod.so
#6  0xb7ff578e in ?? () from /lib/ld-linux.so.2
#7  0xb7ff6247 in ?? () from /lib/ld-linux.so.2
#8  0xb7fa8ca4 in ?? () from /lib/tls/i686/cmov/libdl.so.2
#9  0xb7ff0836 in ?? () from /lib/ld-linux.so.2
#10 0xb7fa909c in ?? () from /lib/tls/i686/cmov/libdl.so.2
#11 0xb7fa8cda in dlclose () from /lib/tls/i686/cmov/libdl.so.2
#12 0x080486b1 in main (argc=1, argv=0xbffff864) at main.c:18


thread 2: 
(gdb) bt
#0  0xb7fe2424 in __kernel_vsyscall ()
#1  0xb7fbe736 in nanosleep () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb7fad92e in printer_loop () from /usr/xenomai/lib/librtdk.so.0
#3  0xb7fb696e in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#4  0xb7f1ba4e in clone () from /lib/tls/i686/cmov/libc.so.6


thread 3: 
(gdb) bt
#0  0xb7fe2424 in __kernel_vsyscall ()
#1  0xb7fbdaf9 in __lll_lock_wait () from /lib/tls/i686/cmov/libpthread.so.0
#2  0xb7fb9149 in _L_lock_839 () from /lib/tls/i686/cmov/libpthread.so.0
#3  0xb7fb8fdb in pthread_mutex_lock () from /lib/tls/i686/cmov/libpthread.so.0
#4  0xb7ff45cd in ?? () from /lib/ld-linux.so.2
#5  0xb7f524a2 in ?? () from /lib/tls/i686/cmov/libc.so.6
#6  0xb7ff0836 in ?? () from /lib/ld-linux.so.2
#7  0xb7f525a1 in ?? () from /lib/tls/i686/cmov/libc.so.6
#8  0xb7f526bb in __libc_dlopen_mode () from /lib/tls/i686/cmov/libc.so.6
#9  0xb7fbfb47 in pthread_cancel_init () from /lib/tls/i686/cmov/libpthread.so.0
#10 0xb7fbfcbd in _Unwind_ForcedUnwind () from /lib/tls/i686/cmov/libpthread.so.0
#11 0xb7fbd788 in __pthread_unwind () from /lib/tls/i686/cmov/libpthread.so.0
#12 0xb7fb79e0 in pthread_exit () from /lib/tls/i686/cmov/libpthread.so.0
#13 0xb7fd8665 in rt_task_trampoline () from /usr/xenomai/lib/libnative.so.3
#14 0xb7fb696e in start_thread () from /lib/tls/i686/cmov/libpthread.so.0
#15 0xb7f1ba4e in clone () from /lib/tls/i686/cmov/libc.so.6


It seems to be another issue into libc6. Or my Xenomai system could be corrupted/misconfigured elsewhere?

Thanks in advance, regards.


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