Question

Why is it dangerous to acquire a lock in an interrupt handler?

Answer 1

`Hey,

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Main problems come when we use locks which go to sleep if the lock can't be obtained, the semaphores. when you try and lock a spinlock, it does not go to sleep, rather it "spins" in a loop trying to lock over and over, this is called busy waiting. obviously, anyone who obtains a spinlock should be very quick with it, or someone else is going to be spinning aimlessly and hogging CPU. on the other hand, if you try and acquire a semaphore that's not available, you will be put to sleep - and that is why can't try and lock a semaphore from an interrupt handler. interrupt handlers are not allowed to sleep, why? b/c sleeping requires the context of a process - the functions you call to invoke a sleep all operate on a globally exported kernel variable called current, a pointer to the currently executing task's task_struct. this pointer is not valid in interrupt code, so if you try to use it by calling a sleep function, ur system will die.

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