On Mon, Jun 15, 2026 at 08:05:58PM +0900, Harry Yoo (Oracle) wrote: > call_rcu() disables IRQs with local_irq_save() to protect its per-cpu > data structures. Therefore, if IRQs are not disabled, they cannot be > corrupted by reentrance into call_rcu(). So fall back to the deferred > path only when !allow_spin && irqs_disabled(). > > The RCU subsystem does not guarantee this contractually, and this > optimization relies on RCU's implementation details. Ideally, it should > be removed once call_rcu_nolock() is supported by the RCU subsystem. > > Link: > https://lore.kernel.org/linux-mm/caadnvqkrvd5zsnekbzzu7w86ghbghuug2pvzpgztngns+fg...@mail.gmail.com > Suggested-by: Alexei Starovoitov <[email protected]> > Signed-off-by: Harry Yoo (Oracle) <[email protected]> > --- > mm/slub.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/slub.c b/mm/slub.c > index b0d38d515386..6a3552b70683 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -6158,8 +6158,8 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj, > bool allow_spin) > if (likely(rcu_sheaf->size < s->sheaf_capacity)) { > rcu_sheaf = NULL; > } else { > - if (unlikely(!allow_spin)) { > - /* call_rcu() cannot be called in an unknown context */ > + /* call_rcu() disables IRQs to protect percpu data structures */ > + if (unlikely(!allow_spin && irqs_disabled())) {
Perhaps this could be more neatly exposed by RCU? something like maybe_in_call_rcu(). Also, it's a bit odd that you're introducing code and then subsequently patching over it with an improvement. Maybe this could be squashed into patch 3? > rcu_sheaf->size--; > local_unlock(&s->cpu_sheaves->lock); > goto fail; > > -- > 2.53.0 > -- Pedro
