Question

do we need a read lock for reading an integer other than if the variable is less than memalign and during some caching situation ?

Answer 1

The analyser assumes that because the address of f1() has been taken, it could be called through that function pointer from any context. If, for example, you have one thread updating x:

lock xlock;
update x;
unlock xlock;

and another thread calls f1() simultaneously through the function pointer, the access to f1() in that second thread won’t be protected by the lock. It could therefore see a partial update of x, or see the update incorrectly ordered with respect to other updates.

The reason why the function pointer matters is that if the address of f1() is never taken, then the analyser can determine exactly where the function is called from. When the address has been taken, it has to assume the worst case.