On Thu, Jul 6, 2023 at 7:07 PM Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote:
>
> Hi,
>
> On 7/6/2023 11:34 AM, Alexei Starovoitov wrote:
> > From: Alexei Starovoitov <ast@xxxxxxxxxx>
> >
> > alloc_bulk() can reuse elements from free_by_rcu_ttrace.
> > Let it reuse from waiting_for_gp_ttrace as well to avoid unnecessary kmalloc().
> >
> > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > ---
> > kernel/bpf/memalloc.c | 16 ++++++++++------
> > 1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
> > index 9986c6b7df4d..e5a87f6cf2cc 100644
> > --- a/kernel/bpf/memalloc.c
> > +++ b/kernel/bpf/memalloc.c
> > @@ -212,6 +212,15 @@ static void alloc_bulk(struct bpf_mem_cache *c, int cnt, int node)
> > if (i >= cnt)
> > return;
> >
> > + for (; i < cnt; i++) {
> > + obj = llist_del_first(&c->waiting_for_gp_ttrace);
> > + if (!obj)
> > + break;
> > + add_obj_to_free_list(c, obj);
> > + }
> > + if (i >= cnt)
> > + return;
>
> I still think using llist_del_first() here is not safe as reported in
> [1]. Not sure whether or not invoking enque_to_free() firstly for
> free_llist_extra will close the race completely. Will check later.
lol. see my reply a second ago in the other thread.
and it's not just waiting_for_gp_ttrace. free_by_rcu_ttrace is similar.
