[PATCH bpf-next v2] samples/bpf: fix possible hang in xdpsock with multiple threads

[PATCH bpf-next v2] samples/bpf: fix possible hang in xdpsock with multiple threads

[Magnus Karlsson]

From: Magnus Karlsson <magnus.karlsson@intel.com>

Fix a possible hang in xdpsock that can occur when using multiple
threads. In this case, one or more of the threads might get stuck in
the while-loop in tx_only after the user has signaled the main thread
to stop execution. In this case, no more Tx packets will be sent, so a
thread might get stuck in the aforementioned while-loop. Fix this by
introducing a test inside the while-loop to check if the benchmark has
been terminated. If so, return from the function.

Fixes: cd9e72b6f210 ("samples/bpf: xdpsock: Add option to specify batch size")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
---
v1->v2:
* Changed break to return

 samples/bpf/xdpsock_user.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index 568f9815bb1b..db0cb73513a5 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
@@ -1275,6 +1275,8 @@ static void tx_only(struct xsk_socket_info *xsk, u32 *frame_nb, int batch_size)
 	while (xsk_ring_prod__reserve(&xsk->tx, batch_size, &idx) <
 				      batch_size) {
 		complete_tx_only(xsk, batch_size);
+		if (benchmark_done)
+			return;
 	}

 	for (i = 0; i < batch_size; i++) {

base-commit: 08c6a2f620e427e879d6ec9329143d6fcd810cd8
--
2.29.0

Re: [PATCH bpf-next v2] samples/bpf: fix possible hang in xdpsock with multiple threads

[Daniel Borkmann]

On 12/10/20 5:34 PM, Magnus Karlsson wrote:
> From: Magnus Karlsson <magnus.karlsson@intel.com>
> 
> Fix a possible hang in xdpsock that can occur when using multiple
> threads. In this case, one or more of the threads might get stuck in
> the while-loop in tx_only after the user has signaled the main thread
> to stop execution. In this case, no more Tx packets will be sent, so a
> thread might get stuck in the aforementioned while-loop. Fix this by
> introducing a test inside the while-loop to check if the benchmark has
> been terminated. If so, return from the function.
> 
> Fixes: cd9e72b6f210 ("samples/bpf: xdpsock: Add option to specify batch size")
> Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>

Applied, thanks!