On 6/30/22 11:58 AM, Magnus Karlsson wrote:

On Wed, Jun 29, 2022 at 4:39 PM Maciej Fijalkowski
[off-list ref] wrote:

quoted

Currently, xsk_socket__delete frees BPF resources regardless of ctx
refcount. Xdpxceiver has a test to verify whether underlying BPF
resources would not be wiped out after closing XSK socket that was bound
to interface with other active sockets. From library's xsk part
perspective it also means that the internal xsk context is shared and
its refcount is bumped accordingly.

After a switch to loading XDP prog based on previously opened XSK
socket, mentioned xdpxceiver test fails with:
not ok 16 [xdpxceiver.c:swap_xsk_resources:1334]: ERROR: 9/"Bad file descriptor

which means that in swap_xsk_resources(), xsk_socket__delete() released
xskmap which in turn caused a failure of xsk_socket__update_xskmap().

To fix this, when deleting socket, decrement ctx refcount before
releasing BPF resources and do so only when refcount dropped to 0 which
means there are no more active sockets for this ctx so BPF resources can
be freed safely.

Please fix this in libxdp too as the bug is present there also.

Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>

[...]

quoted

@@ -1238,7 +1236,10 @@ void xsk_socket__delete(struct xsk_socket *xsk)

         ctx = xsk->ctx;
         umem = ctx->umem;
-       if (ctx->prog_fd != -1) {
+
+       xsk_put_ctx(ctx, true);
+
+       if (!ctx->refcount) {
                 xsk_delete_bpf_maps(xsk);
                 close(ctx->prog_fd);
                 if (ctx->has_bpf_link)

@@ -1257,7 +1258,6 @@ void xsk_socket__delete(struct xsk_socket *xsk)
                 }
         }

-       xsk_put_ctx(ctx, true);

         umem->refcount--;

Applied & also fixed up the double newline. Thanks everyone!