Mauro Salvini wrote:
> 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?
It looks like a typical pthread_join deadlock. The thread you are
joining is locked on a pthread mutex, that some other thread (I would
say, the one calling pthread_join) has. It can not work. You should not
call pthread_join while holding a mutex.
If this is not the issue, would you please take the time to post a
self-contained test case which I can run to reproduce the issue?
Thanks.
--
Gilles.
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