[HDFS-2103] Read lock must be released before acquiring a write lock

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 0.23.0
• Fix Version/s: 0.23.0
• Assignee: Bharath Mundlapudi
• Reporter: Bharath Mundlapudi
• Created: 23/Jun/11 09:09
• Updated: 23/Jun/11 17:41
• Resolved: 23/Jun/11 09:12

Description

In FSNamesystem.getBlockLocationsUpdateTimes function, we have the following code:

    for (int attempt = 0; attempt < 2; attempt++) {
      if (attempt == 0) { // first attempt is with readlock
        readLock();
      }  else { // second attempt is with  write lock
        writeLock(); // writelock is needed to set accesstime
      }

      ...

      if (attempt == 0) {
         continue;
      }

In the above code, readLock is acquired in attempt 0 and if the execution enters in the continue block, then it tries to acquire writeLock before releasing the readLock.