On Wed, Nov 16, 2016 at 10:58:38AM -0800, Kees Cook wrote: > On Wed, Nov 16, 2016 at 2:09 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > On Tue, Nov 15, 2016 at 12:53:35PM -0800, Kees Cook wrote: > >> > >> What should we do about things like this (bpf_prog_put() and callbacks > >> from kernel/bpf/syscall.c): > >> > >> > >> static void bpf_prog_uncharge_memlock(struct bpf_prog *prog) > >> { > >> struct user_struct *user = prog->aux->user; > >> > >> atomic_long_sub(prog->pages, &user->locked_vm); > >> free_uid(user); > >> } > >> > >> static void __bpf_prog_put_rcu(struct rcu_head *rcu) > >> { > >> struct bpf_prog_aux *aux = container_of(rcu, struct bpf_prog_aux, > >> rcu); > >> > >> free_used_maps(aux); > >> bpf_prog_uncharge_memlock(aux->prog); > >> bpf_prog_free(aux->prog); > >> } > >> > >> void bpf_prog_put(struct bpf_prog *prog) > >> { > >> if (atomic_dec_and_test(&prog->aux->refcnt)) > >> call_rcu(&prog->aux->rcu, __bpf_prog_put_rcu); > >> } > >> > >> > >> Not only do we want to protect prog->aux->refcnt, but I think we want > >> to protect user->locked_vm too ... I don't think it's sane for > >> user->locked_vm to be a stats_t ? > > > > Why would you want to mess with locked_vm? You seem of the opinion that > > everything atomic_t is broken, this isn't the case. > > What I mean to say is that while the refcnt here should clearly be > converted to kref or refcount_t, it looks like locked_vm should become > a new stats_t. However, it seems weird for locked_vm to ever wrap > either...
No, its not a statistic. Also, I'm far from convinced stats_t is an actually useful thing to have. refcount_t brought special semantics that clearly are different from regular atomic_t, stats_t would not, so why would it need to exist. Not to mention that you seem over eager to apply it, which doesn't inspire confidence.