Man page 9 : set_bit

set_bit - Atomically set a bit in memory

void set_bit(unsigned int  nr , volatile unsigned long *  addr );

nr
    the bit to set

addr
    the address to start counting from

This function is atomic and may not be reordered. See __set_bit if you do not require the atomic guarantees.

there are no guarantees that this function will not be reordered on non x86 architectures, so if you are writing portable code, make sure not to rely on its reordering guarantees.

Note that nr may be almost arbitrarily large; this function is not restricted to acting on a single-word quantity.