On Fri, Sep 18, 2015 at 10:06:46AM +0100, Dmitry Vyukov wrote: > On Fri, Sep 18, 2015 at 10:51 AM, Peter Zijlstra <[email protected]> wrote: > > As an alternative patch, could we not do: > > > > void put_pid(struct pid *pid) > > { > > struct pid_namespace *ns; > > > > if (!pid) > > return; > > > > ns = pid->numbers[pid->level].ns; > > if ((atomic_read(&pid->count) == 1) || > > atomic_dec_and_test(&pid->count)) { > > > > + smp_read_barrier_depends(); /* ctrl-dep */ > > > > kmem_cache_free(ns->pid_cachep, pid); > > put_pid_ns(ns); > > } > > } > > > > That would upgrade the atomic_read() path to a full READ_ONCE_CTRL(), > > and thereby avoid any of the kmem_cache_free() stores from leaking out. > > And its free, except on Alpha. Whereas the atomic_read_acquire() will > > generate a full memory barrier on whole bunch of archs. > > > What you propose makes sense. > > +Will, Paul > > Can we have something along the lines of: > > #define atomic_read_ctrl(v) READ_ONCE_CTRL(&(v)->counter)
Funnily enough, I had this exact same discussion off-list yesterday afternoon, since I wrote some code relying on a ctrl dependency from an atomic_read to an atomic_xchg_relaxed. So I guess I'm for the addition, but at the same time, could we make atomic_read and atomic_set generic too? Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
