cagney <[email protected]> added the comment:
(disclaimer: I'm mashing my high level backtraces in with @jwiki's low level
backtraces)
The Python backtrace shows the deadlocked process called 'f' which then
'called':
import ctypes
which, in turn 'called':
from _ctypes import Union, Structure, Array
and that hung.
The low-level back-trace shows it was trying to acquire a lock (no surprises
there); but the surprise is that it is inside of dlopen() trying to load
'_ctypes...so'!
#11 __dlopen (file=file@entry=0x7f398da4b050
"_ctypes.cpython-37m-x86_64-linux-gnu.so", mode=<optimized out>) at dlopen.c:87
...
#3 _dl_map_object_from_fd (name="_ctypes.cpython-37m-x86_64-linux-gnu.so",
origname=origname@entry=0x0, fd=-1, fbp=<optimized out>, realname=<optimized
out>, loader=loader@entry=0x0, l_type=<optimized out>, mode=<optimized out>,
stack_endp=<optimized out>, nsid=<optimized out>) at dl-load.c:1413
#2 _dl_add_to_namespace_list (new=0x55f8b8f34540, nsid=0) at dl-object.c:34
#1 __GI___pthread_mutex_lock (mutex=0x7f3991fb9970 <_rtld_global+2352>) at
../nptl/pthread_mutex_lock.c:115
and the lock in question (assuming my sources roughly match above) seems to be:
/* We modify the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));
presumably a thread in the parent held this lock at the time of the fork.
If one of the other children also has the lock pre-acquired then this is
confirmed (unfortunately not having the lock won't rebut the theory).
So, any guesses as to what dl related operation was being performed by the
parent?
----
I don't think the remaining processes are involved (and I've probably got 4 in
total because my machine has 4 cores).
8976 - this acquired the multi-process semaphore and is blocked in '_recv'
awaiting further instructions
8978, 8977 - these are blocked waiting for above to free the multi-process
semaphore
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<https://bugs.python.org/issue35866>
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