[PATCH AUTOSEL 5.8 061/132] samples/bpf: Fix possible deadlock in xdpsock

[Sasha Levin]

From: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>

[ Upstream commit 5a2a0dd88f0f267ac5953acd81050ae43a82201f ]

Fix a possible deadlock in the l2fwd application in xdpsock that can
occur when there is no space in the Tx ring. There are two ways to get
the kernel to consume entries in the Tx ring: calling sendto() to make
it send packets and freeing entries from the completion ring, as the
kernel will not send a packet if there is no space for it to add a
completion entry in the completion ring. The Tx loop in l2fwd only
used to call sendto(). This patches adds cleaning the completion ring
in that loop.

Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Link: https://lore.kernel.org/bpf/1599726666-8431-3-git-send-email-magnus.karlsson@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 samples/bpf/xdpsock_user.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index c91e91362a0c6..a2f8033ab9c3d 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
@@ -1028,6 +1028,7 @@ static void l2fwd(struct xsk_socket_info *xsk, struct pollfd *fds)
 	while (ret != rcvd) {
 		if (ret < 0)
 			exit_with_error(-ret);
+		complete_tx_l2fwd(xsk, fds);
 		if (xsk_ring_prod__needs_wakeup(&xsk->tx))
 			kick_tx(xsk);
 		ret = xsk_ring_prod__reserve(&xsk->tx, rcvd, &idx_tx);
-- 
2.25.1