Deadlock creating >5 servers at once using xenapi driver

Bug #924918 reported by Johannes Erdfelt on 2012-02-01
This bug affects 1 person
Affects Status Importance Assigned to Milestone
OpenStack Compute (nova)
Johannes Erdfelt

Bug Description

A deadlock can occur when a compute node is working on more than 5 servers at once. This only affects systems using the xenapi driver.

The problem is caused by a nested use of _get_session(). If multiple greenthreads are attempting to communicate with dom0 at once, then the outer call to _get_session() can end up with all of the sessions acquired leaving the inner calls to _get_session() waiting for one of the outer calls to release.

Changed in nova:
assignee: nobody → Johannes Erdfelt (johannes.erdfelt)

Fix proposed to branch: master

Changed in nova:
status: New → In Progress

Submitter: Jenkins
Branch: master

commit 093e4d38d511c7bb8d48fceebbfd8e350b533075
Author: Johannes Erdfelt <email address hidden>
Date: Wed Feb 1 17:07:16 2012 +0000

    Make sure multiple calls to _get_session() aren't nested

    Fixes bug 924918

    async_call_plugin() acquires a xenapi session as does the nested call to
    get_xenapi_host(). This can cause a deadlock if multiple greenthreads
    all block waiting for the outer sessions to be freed to allocate the
    inner session. This change moves the call to get_xenapi_host() to outside
    the with statement to ensure calls to _get_session() aren't nested.

    Change-Id: I8f5490f40a9ccaf74a276187f66519a5d5f52b2e

Changed in nova:
status: In Progress → Fix Committed
Thierry Carrez (ttx) on 2012-02-29
Changed in nova:
milestone: none → essex-4
status: Fix Committed → Fix Released
Thierry Carrez (ttx) on 2012-04-05
Changed in nova:
milestone: essex-4 → 2012.1
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