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docs: add another strace recipe

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David Wilson 2019-01-22 11:59:56 +00:00
parent f52f7f6a62
commit 3e255129ab
1 changed files with 19 additions and 0 deletions
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docs/ansible.rst
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@ -1134,6 +1134,25 @@ cases `faulthandler <https://faulthandler.readthedocs.io/>`_ may be used:
of the stacks, along with a description of the last task executing prior to of the stacks, along with a description of the last task executing prior to
the hang. the hang.
It is possible the hang occurred in a process on a target. If ``strace`` is
available, look for the host name not listed in Ansible output as reporting a
result for the most recent task, log into it, and use ``strace -ff -p <pid>``
on each process whose name begins with ``mitogen:``::
$ strace -ff -p 29858
strace: Process 29858 attached with 3 threads
[pid 29864] futex(0x55ea9be52f60, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 29860] restart_syscall(<... resuming interrupted poll ...> <unfinished ...>
[pid 29858] futex(0x55ea9be52f60, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff
^C
$
This shows one thread waiting on IO (``poll``) and two more waiting on the same
lock. It is taken from a real example of a deadlock due to a forking bug.
Please include any such information for all processes that you are able to
collect in any bug report.
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