“Double fault” doesnt mean the one you know in Tennis. Here it is an EXCEPTION that occurs in the CPU. Double fault occurs if the processor encounters a problem while trying to service a pending interrupt or exception. These double faults can only happen due to kernel bugs.
Double faults may occur due to the following reasons.
In the x86 architecture,

1 . A double fault indicates a problem with the Interrupt Descriptor Table (IDT). For example, if an interrupt occurs but the segment the processor is supposed to switch to is invalid, double fault shall occur.
2 .  When the interrupt is going to a higher privilege level. In that case, the Task State Segment is used to find the new stack pointer. If the processor encounters a problem when reading the TSS, it shall trigger a double fault.
In SPARC or PowerPC architecture,
3 . These processors generally save state to predefined as well as reserved machine registers. A double fault shall happen where another exception happens while the processor is still using the content of these registers to process the exception.
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If the processor encounters a problem when calling the double fault handler, a triple fault is generated as well as the processor shuts down. People having their computer spontaneously rebooting are an estimated all likely experiencing triple faults.