NAME
__test_and_clear_bit - Clear a bit and return its old value
SYNOPSIS
bool __test_and_clear_bit(long 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