ZanderXu opened a new pull request, #4945:
URL: https://github.com/apache/hadoop/pull/4945
### Description of PR
When patching the fine-grained locking of datanode, I found that
`addVolume` will hold the write block of the BP lock to scan the new volume to
get the blocks. If we try to add one full volume that was fixed offline before,
i will hold the write lock for a long time.
The related code as bellows:
```
for (final NamespaceInfo nsInfo : nsInfos) {
String bpid = nsInfo.getBlockPoolID();
try (AutoCloseDataSetLock l = lockManager.writeLock(LockLevel.BLOCK_POOl,
bpid)) {
fsVolume.addBlockPool(bpid, this.conf, this.timer);
fsVolume.getVolumeMap(bpid, tempVolumeMap, ramDiskReplicaTracker);
} catch (IOException e) {
LOG.warn("Caught exception when adding " + fsVolume +
". Will throw later.", e);
exceptions.add(e);
}
}
```
And I noticed that this lock is added by
[HDFS-15382](https://issues.apache.org/jira/browse/HDFS-15382), means that this
logic was not with lock before.
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