On Tue, Oct 11, 2022 at 03:11:27PM +0800, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> Local storage map is accessible for both sleepable and normal bpf
> program, so its memory is freed by using both call_rcu_tasks_trace() and
> kfree_rcu() to wait for both RCU-tasks-trace grace period and RCU grace
> period to expire.
>
> However According to the current implementation of RCU-tasks-trace, one
> RCU-tasks-trace grace period waits for one RCU grace period, so there is
> no need to call kfree_rcu(), it is safe to call kfree() directly.
Again, this is true, but this is an implementation detail that is not
guaranteed in future versions of the kernel. But if this additional
call_rcu() is causing trouble, I could add some API member that
returned true in kernels where it does happen to be the case that
call_rcu_tasks_trace() implies a call_rcu()-style grace period.
The BPF local storage code could then complain or adapt, as appropriate.
Again, thoughts?
Thanx, Paul
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
> ---
> kernel/bpf/bpf_local_storage.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
> index 802fc15b0d73..18a2dd611635 100644
> --- a/kernel/bpf/bpf_local_storage.c
> +++ b/kernel/bpf/bpf_local_storage.c
> @@ -84,20 +84,26 @@ bpf_selem_alloc(struct bpf_local_storage_map *smap, void *owner,
> return NULL;
> }
>
> +/* Now RCU Tasks grace period implies RCU grace period, so no need to call
> + * kfree_rcu(), just call kfree() directly.
> + */
> void bpf_local_storage_free_rcu(struct rcu_head *rcu)
> {
> struct bpf_local_storage *local_storage;
>
> local_storage = container_of(rcu, struct bpf_local_storage, rcu);
> - kfree_rcu(local_storage, rcu);
> + kfree(local_storage);
> }
>
> +/* Now RCU Tasks grace period implies RCU grace period, so no need to call
> + * kfree_rcu(), just call kfree() directly.
> + */
> static void bpf_selem_free_rcu(struct rcu_head *rcu)
> {
> struct bpf_local_storage_elem *selem;
>
> selem = container_of(rcu, struct bpf_local_storage_elem, rcu);
> - kfree_rcu(selem, rcu);
> + kfree(selem);
> }
>
> /* local_storage->lock must be held and selem->local_storage == local_storage.
> --
> 2.29.2
>
