It's the same thing as you read:
THREAD size is 8kb so the operation looks like the following:
current_stack_pointer & ~(8191) == current_stack_pointet & 0xFFFFFE00
(last 13 bits are 0)

Ok. Got it.

But how ANDing it with current stack pointer points to the address of
thread_info structure.
Suppose stack is growing from higher to lower memory address.

Thanks,
Vijay