Hello, Hillf! > Hi Ulad > > Good work with a nit. > Thank you :)
> On Mon, Oct 16, 2023 at 1:30 PM Uladzislau Rezki (Sony) <[email protected]> > wrote: > > +static void rcu_sr_normal_gp_init(void) > > +{ > > + struct llist_node *llnode, *rcu; > > + int ret; > > + > > + if (llist_empty(&sr.curr)) > > + return; > > This empty check erases the curr_tail race below instead of > atomic_inc_return(&sr.active), because llist_add() will never return true > after this check. > I use "active" counter to guarantee that a tail was updated in the rcu_sr_normal_add_req(), i.e. the list might be not empty whereas the tail updating might be in progress. llist_add() success and the task gets preemted as an example. Or i miss your point? If so, i appreciate if you clarify it in more detail. > > + > > + /* > > + * A waiting list of GP should be empty on this step, > > + * since a GP-kthread, rcu_gp_init() -> gp_cleanup(), > > + * rolls it over. If not, it is a BUG, warn a user. > > + */ > > + WARN_ON_ONCE(!llist_empty(&sr.wait)); > > + > > + /* > > + * Obtain a tail of current active users. It is guaranteed > > + * that if we are only one active user and the list is not > > + * empty, the tail has already been updated. > > + */ > > + ret = atomic_inc_return(&sr.active); > > Replacing atomic_inc_return() with smp_mb() cuts sr.active off. > But here we would like to know that we were only one user + not empty list gurantees that a tail is ready. Thank you for your comments! -- Uladzislau Rezki
