D.2.7.5 Interrupt from Dynticks Idle Mode
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D.2.7.5 Interrupt from Dynticks Idle Mode

Interrupts from dynticks idle mode are handled by rcu_irq_enter() and rcu_irq_exit(). The rcu_irq_enter() function increments the per-CPU dynticks_nesting variable, and, if the prior value was zero, also increments the dynticks per-CPU variable (which must then have an odd-numbered value).

The rcu_irq_exit() function decrements the per-CPU dynticks_nesting variable, and, if the new value is zero, also increments the dynticks per-CPU variable (which must then have an even-numbered value).

Note that entering an irq handler exits dynticks idle mode and vice versa. This enter/exit anti-correspondence can cause much confusion. You have been warned.