On Fri, Oct 12, 2018 at 7:31 PM, Alexei Starovoitov alexei.starovoitov@gmail.com wrote:
On Fri, Oct 12, 2018 at 03:54:27AM -0700, Daniel Colascione wrote:
The map-in-map frequently serves as a mechanism for atomic snapshotting of state that a BPF program might record. The current implementation is dangerous to use in this way, however, since userspace has no way of knowing when all programs that might have retrieved the "old" value of the map may have completed.
This change ensures that map update operations on map-in-map map types always wait for all references to the old map to drop before returning to userspace.
Signed-off-by: Daniel Colascione dancol@google.com
kernel/bpf/syscall.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 8339d81cba1d..d7c16ae1e85a 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -741,6 +741,18 @@ static int map_lookup_elem(union bpf_attr *attr) return err; }
+static void maybe_wait_bpf_programs(struct bpf_map *map) +{
/* Wait for any running BPF programs to complete so that* userspace, when we return to it, knows that all programs* that could be running use the new map value.*/if (map->map_type == BPF_MAP_TYPE_HASH_OF_MAPS ||map->map_type == BPF_MAP_TYPE_ARRAY_OF_MAPS) {synchronize_rcu();}extra {} were not necessary. I removed them while applying to bpf-next. Please run checkpatch.pl next time. Thanks
Thanks Alexei for taking it. Me and Lorenzo were discussing that not having this causes incorrect behavior for apps using map-in-map for this. So I CC'd stable as well.
-Joel