Jann Horn <jannh@xxxxxxxxxx> wrote:
> > + if (!s->s_watchers) {
>
> READ_ONCE() ?
I'm not sure it matters. It can only be set once, and the next time we read
it we're inside the lock. And at this point, I don't actually dereference it,
and if it's non-NULL, it's not going to change.
> > + ret = add_watch_to_object(watch, s->s_watchers);
> > + if (ret == 0) {
> > + spin_lock(&sb_lock);
> > + s->s_count++;
> > + spin_unlock(&sb_lock);
>
> Where is the corresponding decrement of s->s_count? I'm guessing that
> it should be in the ->release_watch() handler, except that there isn't
> one...
Um. Good question. I think this should do the job:
static void sb_release_watch(struct watch *watch)
{
put_super(watch->private);
}
And this then has to be set later:
init_watch_list(wlist, sb_release_watch);
> > + } else {
> > + ret = -EBADSLT;
> > + if (READ_ONCE(s->s_watchers)) {
>
> (Nit: I don't get why you do a lockless check here before taking the
> lock - it'd be more straightforward to take the lock first, and it's
> not like you want to optimize for the case where someone calls
> sys_watch_sb() with invalid arguments...)
Fair enough. I'll remove it.
> > +#ifdef CONFIG_SB_NOTIFICATIONS
> > + if (unlikely(s->s_watchers)) {
>
> READ_ONCE() ?
Shouldn't matter. It's only read once and then a decision is made on it
immediately thereafter. And if it's non-NULL, the value cannot change
thereafter.
David
