Messages in this thread | | | Date | Fri, 02 Mar 2012 09:11:47 +0000 | From | "Jan Beulich" <> | Subject | Re: [RFC patch] cmpxchg_double: remove local variables to get better performance |
| |
>>> On 02.03.12 at 10:00, Alex Shi <alex.shi@intel.com> wrote: > Yes, we can use cast for intermediate data. And actually, current kernel > has live mis-used case on cmpxchg(), that I plan to point out too. > > -- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -203,12 +203,12 @@ static bool make_all_cpus_request(struct kvm *kvm, > unsigned int req) > > void kvm_flush_remote_tlbs(struct kvm *kvm) > { > - int dirty_count = kvm->tlbs_dirty; > + long dirty_count = kvm->tlbs_dirty; > > smp_mb(); > if (make_all_cpus_request(kvm, KVM_REQ_TLB_FLUSH)) > ++kvm->stat.remote_tlb_flush; > - cmpxchg(&kvm->tlbs_dirty, dirty_count, 0); > + cmpxchg(&kvm->tlbs_dirty, dirty_count, 0L);
Indeed - the cmpxchg would fail if the value doesn't fit. But this is not to say that in certain cases it isn't valid to pass an int for the second and/or third argument. (And quite likely the issue here is theoretical only anyway.)
In particular, requiring an L suffix here on literals should be avoided.
Jan
> }
| |