in hbase 0.98.10, class HRegionServer method openRegion line 3827
when RS open region, if this region is already opened by RS, we will check hbase:meta to see if hbase:meta is updated. but, if the RS is opening hbase:meta, then MetaReader.getRegion will return null(we do not store hbase:meta data in table hbase:meta), and lead to nullPointerException we can reproduce this problem as follows: 1. master assign hbase:meta 2. RS open hbase:meta slowly, master timeout(may because of high load or network problem), 3. master send open region request again(RS is still opening hbase:meta, and opened) 4. RS will throw NullPointerException and hmaster will retry forever
