On Mon, Oct 12, 2026 at 10:54:43PM +0200, Max Kellermann wrote: > Move some code from hlist_nulls_add_tail_rcu() to the new function > hlist_nulls_add_behind_rcu() for callers that already know the last > node of an `hlist_nulls` list, to allow constant-time appends. > > Signed-off-by: Max Kellermann <[email protected]>
I am assuming that this commit should take the same path as the rest of them. So: Reviewed-by: Paul E. McKenney <[email protected]> > --- > include/linux/rculist_nulls.h | 36 +++++++++++++++++++++++++++++------ > 1 file changed, 30 insertions(+), 6 deletions(-) > > diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h > index a97c3bcb1656..054e477dd093 100644 > --- a/include/linux/rculist_nulls.h > +++ b/include/linux/rculist_nulls.h > @@ -115,6 +115,33 @@ static inline void hlist_nulls_add_head_rcu(struct > hlist_nulls_node *n, > WRITE_ONCE(first->pprev, &n->next); > } > > +/** > + * hlist_nulls_add_behind_rcu - append after the last list entry > + * @n: the new element to add to the hash list. > + * @last: the last element in the list. > + * > + * Adds the specified element after @last while permitting racing RCU > + * traversals. @last must be the last list entry, with its next > + * pointer holding the terminating nulls marker. > + * > + * The caller must take whatever precautions are necessary > + * (such as holding appropriate locks) to avoid racing > + * with another list-mutation primitive, such as hlist_nulls_add_head_rcu() > + * or hlist_nulls_del_rcu(), running on this same list. > + * However, it is perfectly legal to run concurrently with > + * the _rcu list-traversal primitives, such as > + * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency > + * problems on Alpha CPUs. Regardless of the type of CPU, the > + * list-traversal primitive must be guarded by rcu_read_lock(). > + */ > +static inline void hlist_nulls_add_behind_rcu(struct hlist_nulls_node *n, > + struct hlist_nulls_node *last) > +{ > + WRITE_ONCE(n->next, last->next); > + WRITE_ONCE(n->pprev, &last->next); > + rcu_assign_pointer(hlist_nulls_next_rcu(last), n); > +} > + > /** > * hlist_nulls_add_tail_rcu > * @n: the element to add to the hash list. > @@ -143,13 +170,10 @@ static inline void hlist_nulls_add_tail_rcu(struct > hlist_nulls_node *n, > for (i = h->first; !is_a_nulls(i); i = i->next) > last = i; > > - if (last) { > - WRITE_ONCE(n->next, last->next); > - WRITE_ONCE(n->pprev, &last->next); > - rcu_assign_pointer(hlist_nulls_next_rcu(last), n); > - } else { > + if (last) > + hlist_nulls_add_behind_rcu(n, last); > + else > hlist_nulls_add_head_rcu(n, h); > - } > } > > /* after that hlist_nulls_del will work */ > -- > 2.47.3 > >
