[Pacemaker] Pacemaker does not handler demote/promote atomically

[hj lee]

Hi,

In the typical multi-state resource agent, it changes master score on demote
or promote. Each change in master score triggers PE calculation. Suppose the
following scenario.
1. Pacemaker initiates demote/promote
2. demote is issued and lower the master score on the demoted node.
3. promote is issued and increases the master score on the promoted node.

The PE calculation can be kicked off between 2 and 3, then the pacemaker
will see two slaves in the moment. Depending on the master score it sees at
the moment, the pacemaker may promote the old master.

I think the pacemaker should handle demote/promote atomically, meaning it
should prevent any PE calculation between demote and promote.

Thanks
hj
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