Clifford Jansen created PROTON-2483:
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Summary: TSAN reported potential deadlock in epoll proactor when
run via Qpid Dispatch router.
Key: PROTON-2483
URL: https://issues.apache.org/jira/browse/PROTON-2483
Project: Qpid Proton
Issue Type: Bug
Components: proton-c
Affects Versions: proton-c-0.36.0
Environment: linux epoll
Reporter: Clifford Jansen
Assignee: Clifford Jansen
The traces are incomplete but the 4 way thread tangle can be inferred as
follows:
A: pn_proactor_set_timeout() (p->task.mutex + tm->task.mutex)
B: pni_timer_manager_process() (tm->task.mutex + tm->deletion_mutex)
C: pni_connection_timeout() (tm->deletion_mutex + pc1->task.mutex)
D: proactor_remove() (pc1->task.mutex + p->task.mutex)
While this particular trace is a false positive (D occurs after all other
threads have been joined and there are no competing threads to complete the
circle), the lock ordering is clearly asking for eventual trouble.
The proactor set_timeout and cancel_timeout API calls do not need to hold the
proactor task lock while interacting with the timer manager, but do so as a
convenience to prevent collisions between simultaneous sets/cancels. A
separate lock can achieve that purpose, stopping A from participating in the
potential deadlock.
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