[PATCH bpf-next] xsk: simplify AF_XDP socket teardown

[PATCH bpf-next] xsk: simplify AF_XDP socket teardown

[bjorn.topel]

From: Björn Töpel <bjorn.topel@intel.com>

Prior this commit, when the struct socket object was being released,
the UMEM did not have its reference count decreased. Instead, this was
done in the struct sock sk_destruct function.

There is no reason to keep the UMEM reference around when the socket
is being orphaned, so in this patch the xdp_put_mem is called in the
xsk_release function. This results in that the xsk_destruct function
can be removed!

Note that, it still holds that a struct xsk_sock reference might still
linger in the XSKMAP after the UMEM is released, e.g. if a user does
not clear the XSKMAP prior to closing the process. This sock will be
in a "released" zombie like state, until the XSKMAP is removed.

Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
---
 net/xdp/xsk.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
index 07156f43d295..a03268454a27 100644
--- a/net/xdp/xsk.c
+++ b/net/xdp/xsk.c
@@ -366,6 +366,7 @@ static int xsk_release(struct socket *sock)
 
 	xskq_destroy(xs->rx);
 	xskq_destroy(xs->tx);
+	xdp_put_umem(xs->umem);
 
 	sock_orphan(sk);
 	sock->sk = NULL;
@@ -713,18 +714,6 @@ static const struct proto_ops xsk_proto_ops = {
 	.sendpage	= sock_no_sendpage,
 };
 
-static void xsk_destruct(struct sock *sk)
-{
-	struct xdp_sock *xs = xdp_sk(sk);
-
-	if (!sock_flag(sk, SOCK_DEAD))
-		return;
-
-	xdp_put_umem(xs->umem);
-
-	sk_refcnt_debug_dec(sk);
-}
-
 static int xsk_create(struct net *net, struct socket *sock, int protocol,
 		      int kern)
 {
@@ -751,9 +740,6 @@ static int xsk_create(struct net *net, struct socket *sock, int protocol,
 
 	sk->sk_family = PF_XDP;
 
-	sk->sk_destruct = xsk_destruct;
-	sk_refcnt_debug_inc(sk);
-
 	sock_set_flag(sk, SOCK_RCU_FREE);
 
 	xs = xdp_sk(sk);
-- 
2.19.1

Re: [PATCH bpf-next] xsk: simplify AF_XDP socket teardown

[Daniel Borkmann]

On 12/19/2018 01:09 PM, bjorn.topel@gmail.com wrote:
> From: Björn Töpel <bjorn.topel@intel.com>
> 
> Prior this commit, when the struct socket object was being released,
> the UMEM did not have its reference count decreased. Instead, this was
> done in the struct sock sk_destruct function.
> 
> There is no reason to keep the UMEM reference around when the socket
> is being orphaned, so in this patch the xdp_put_mem is called in the
> xsk_release function. This results in that the xsk_destruct function
> can be removed!
> 
> Note that, it still holds that a struct xsk_sock reference might still
> linger in the XSKMAP after the UMEM is released, e.g. if a user does
> not clear the XSKMAP prior to closing the process. This sock will be
> in a "released" zombie like state, until the XSKMAP is removed.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>

Applied, thanks!