Fix condition in PFSAgent where DoSetAttr() needs to speculatively re…

…ference a fileInode

Unfortunately, the sanity check enforced that fileInode.reference() was only called from DoWrite()
where fileInode.references *WOULD* always be non-zero.

This change switches DoSetAttr() to instead use the referenceFileInode() func to increment the
fileInode.references... possibly from zero. The fact that it will cause a fileInode to be created in
the very small chance it was removed just after DoSetAttr() found it but before the call to
referenceFileInode() is ok... no damage will be done.

pfsagentd/fission.go

@@ -517,7 +517,14 @@ func (dummy *globalsStruct) DoSetAttr(inHeader *fission.InHeader, setAttrIn *fis
 	globals.Unlock()
 
 	if cachedFileInodeCase {
-		fileInode.reference()
+		// Calling referenceFileInode() here even though we "know" fileInode to avoid the
+		// sanity check otherwise valid where fileInode.references should not be zero.
+		//
+		// Note that, to avoid any race ambiguity, we will use the fileInode returned
+		// from referenceFileInode() moving forward on the off-chance the one we fetched
+		// from globals.fileInodeMap was removed just after the globals.Unlock() call.
+
+		fileInode = referenceFileInode(inode.InodeNumber(inHeader.NodeID))
 
 		fileInode.doFlushIfNecessary()
 	}