bpf: offload: add comment warning developers about double destroy

Offload state may get destroyed either because the device for which
it was constructed is going away, or because the refcount of bpf
program itself has reached 0.  In both of those cases we will call
__bpf_prog_offload_destroy() to unlink the offload from the device.
We may in fact call it twice, which works just fine, but we should
make clear this is intended and caution others trying to extend the
function.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index 2816feb38be16a0137bc7aa351606f24466c55e1..fd696d3dd429ed1c8d2759fcd4fab971c69737af 100644 (file)
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -85,6 +85,10 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
        struct bpf_dev_offload *offload = prog->aux->offload;
        struct netdev_bpf data = {};
 
+       /* Caution - if netdev is destroyed before the program, this function
+        * will be called twice.
+        */
+
        data.offload.prog = prog;
 
        if (offload->verifier_running)