centos man page for __test_and_set_bit

__TEST_AND_SET_BIT(9)					     Basic C Library Functions					     __TEST_AND_SET_BIT(9)

NAME
       __test_and_set_bit - Set a bit and return its old value

SYNOPSIS
       int __test_and_set_bit(int nr, volatile unsigned long * addr);

ARGUMENTS
       nr
	   Bit to set

       addr
	   Address to count from

DESCRIPTION
       This operation is non-atomic and can be reordered. If two examples of this operation race, one can appear to succeed but actually fail. You
       must protect multiple accesses with a lock.

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						     __TEST_AND_SET_BIT(9)