__test_and_clear_bit(9) centos man page | unix.com

__TEST_AND_CLEAR_BIT(9) 				     Basic C Library Functions					   __TEST_AND_CLEAR_BIT(9)

NAME
       __test_and_clear_bit - Clear a bit and return its old value

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

ARGUMENTS
       nr
	   Bit to clear

       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.

NOTE
       the operation is performed atomically with respect to the local CPU, but not other CPUs. Portable code should not rely on this behaviour.
       KVM relies on this behaviour on x86 for modifying memory that is also

ACCESSED FROM A HYPERVISOR ON THE SAME CPU IF RUNNING IN A VM
       don't change this without also updating arch/x86/kernel/kvm.c

COPYRIGHT
Kernel Hackers Manual 3.10					     June 2014						   __TEST_AND_CLEAR_BIT(9)