On Wed, Jul 29, 2020 at 07:48 PM CEST, Andrii Nakryiko wrote:
On Wed, Jul 29, 2020 at 7:29 AM Jakub Sitnicki jakub@cloudflare.com wrote:
On Wed, Jul 29, 2020 at 06:09 AM CEST, Andrii Nakryiko wrote:
[...]
+/*
- Trigger synchronize_cpu() in kernel.
Nit: synchronize_*r*cu().
welp, yeah
- ARRAY_OF_MAPS/HASH_OF_MAPS lookup/update operations trigger
- synchronize_rcu(), if looking up/updating non-NULL element. Use this fact
- to trigger synchronize_cpu(): create map-in-map, create a trivial ARRAY
- map, update map-in-map with ARRAY inner map. Then cleanup. At the end, at
- least one synchronize_rcu() would be called.
- */
That's a cool trick. I'm a bit confused by "looking up/updating non-NULL element". It looks like you're updating an element that is NULL/unset in the code below. What am I missing?
I was basically trying to say that it has to be a successful lookup or update. For lookup that means looking up non-NULL (existing) entry. For update -- setting valid inner map FD.
Not sure fixing this and typo above is worth it to post v5.
I just wanted to understand that the helper is working as intended. It seems handy. I agree that it's not worth respinning the patches just for this.
+static int kern_sync_rcu(void) +{
int inner_map_fd, outer_map_fd, err, zero = 0;inner_map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, 4, 4, 1, 0);if (CHECK(inner_map_fd < 0, "inner_map_create", "failed %d\n", -errno))return -1;outer_map_fd = bpf_create_map_in_map(BPF_MAP_TYPE_ARRAY_OF_MAPS, NULL,sizeof(int), inner_map_fd, 1, 0);if (CHECK(outer_map_fd < 0, "outer_map_create", "failed %d\n", -errno)) {close(inner_map_fd);return -1;}err = bpf_map_update_elem(outer_map_fd, &zero, &inner_map_fd, 0);if (err)err = -errno;CHECK(err, "outer_map_update", "failed %d\n", err);close(inner_map_fd);close(outer_map_fd);return err;+}
[...]
trimming's good ;)
You caught me. Just being lazy. No excuses :-)