__test_and_clear_bit — Clear a bit and return its old value


bool __test_and_clear_bit (long nr,
 volatile unsigned long * addr);


long nr

Bit to clear

volatile unsigned long * addr

Address to count from


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.


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