Avoid getting meta sync lock if no need

[secfree]

What changes are proposed in this pull request?

Avoid getting meta sync lock if no need.

Why are the changes needed?

After backporting #16241, "ls /" encountered the following exception

2023-03-30 14:00:51,657 ERROR FileSystemMasterClientServiceHandler - Exit (Error): ListStatus: request=path: "/"
options {
  loadMetadataType: ONCE
  commonOptions {
    syncIntervalMs: 86400000
    ttl: -1
    ttlAction: DELETE
  }
  recursive: false
  loadMetadataOnly: false
}

java.lang.RuntimeException: Call cancelled by trackers: GRPC_CLIENT_TRACKER
        at alluxio.master.file.RpcContext.throwIfCancelled(RpcContext.java:107)
        at alluxio.master.file.InodeSyncStream.sync(InodeSyncStream.java:322)
        at alluxio.master.file.DefaultFileSystemMaster.syncMetadata(DefaultFileSystemMaster.java:3816)
        at alluxio.master.file.DefaultFileSystemMaster.listStatus(DefaultFileSystemMaster.java:1042)
        ...

We found that "ls /" was waiting for the WRITE lock of "/" in MetadataSyncLockManager even it did not need to sync metadata. As other clients were "ls" other paths and they hold READ lock on "/", "ls /" got stuck.

Does this PR introduce any user facing changes?

NO

[secfree]

cc @elega

[ChunxuTang]

Thanks for the contribution!

[yyongycy]

Did you see this issue in the master branch? If not, why is this only triggered in your branch?
On the other hand, "ls /" should be quite frequently. If this is blocked, others should also see that.

[yyongycy]

@tcrain any thoughts?

[secfree]

Did you see this issue in the master branch? If not, why is this only triggered in your branch?

No. We didn't use the master branch in our production clusters.

[secfree]

On the other hand, "ls /" should be quite frequently. If this is blocked, others should also see that.

I have not tested that if the master branch also has the following problem:

We found that "ls /" was waiting for the WRITE lock of "/" in MetadataSyncLockManager even it did not need to sync metadata.

If yes, then the PR is still needed. If no, then it may just be an issue in our internal branch. I think this point can be confirmed from code.

[yyongycy]

On the other hand, "ls /" should be quite frequently. If this is blocked, others should also see that.

I have not tested that if the master branch also has the following problem:

We found that "ls /" was waiting for the WRITE lock of "/" in MetadataSyncLockManager even it did not need to sync metadata.

If yes, then the PR is still needed. If no, then it may just be an issue in our internal branch. I think this point can be confirmed from code.

Could you please help double check to see if the master branch has this problem? If the master branch has no such problem, there must be some problem someplace else triggered this issue in your branch.

[yyongycy]

Since yimin confirmed, I am fine with this pr. Thanks for fixing it.

[yyongycy]

LGTM

[yyongycy]

alluxio-bot, merge this please