does anyone have some idea what is Task Gate segment good for? It seems to contain only reference to Task Selector. What is advantage of task gate over using selector directly?

While I'm not certain, I think the Task Gate is a protection mechanism for the TSS.

Here is an good article on Task Gates and task switching.

thanks, it will be helpful.

By the way, I already figured out. Task Segment can be only present in GDT, and task gate can be used in IDT too, when interrupt handler should execute within different task.

Maybe it has also other uses i am not aware of.