When a process is waiting on an external event/interrupt to occur, it is removed from the run queue and placed on a wait queue. The tasks on a given wait queue are woken up, at which point the tasks verify the condition they are waiting for and either resume sleep or remove themselves from the wait queue and set themselves back to TASK_RUNNING.

here I have doubt that external event/ i.e interrupt is occured so my ISR set the flag. before the process is in running state. What is effect of this?

Possibility 1: Whenever your process enters the running state, and scheduled to run, Is this process directly executed/ or again it wait for an /interrupt to occur ?

Little more details my read call wait on wait_event_interruptible if the interrupt is occurred before the read call. What is the efffect of this?

Possibility 1: read call again wait for an interrupt to occur

Possibility 2: whenever the read call isssued run directly because already the flagis set by ISR.

Any suggestion/links is greatly appreciated.

Regards
Ravime