[PATCH 5.17 0664/1126] samples/bpf, xdpsock: Fix race when running for fix duration of time

Greg Kroah-Hartman
2022-04-05T09:53:03Z

From: Niklas Söderlund <niklas.soderlund@corigine.com>

[ Upstream commit 8fa42d78f6354bb96ad3a079dcbef528ca9fa9e0 ]

When running xdpsock for a fix duration of time before terminating
using --duration=<n>, there is a race condition that may cause xdpsock
to terminate immediately.

When running for a fixed duration of time the check to determine when to
terminate execution is in is_benchmark_done() and is being executed in
the context of the poller thread,

if (opt_duration > 0) {
unsigned long dt = (get_nsecs() - start_time);

if (dt >= opt_duration)
benchmark_done = true;
}

However start_time is only set after the poller thread have been
created. This leaves a small window when the poller thread is starting
and calls is_benchmark_done() for the first time that start_time is not
yet set. In that case start_time have its initial value of 0 and the
duration check fails as it do not correlate correctly for the
applications start time and immediately sets benchmark_done which in
turn terminates the xdpsock application.

Fix this by setting start_time before creating the poller thread.

Fixes: d3f11b018f6c ("samples/bpf: xdpsock: Add duration option to specify how long to run")
Signed-off-by: Niklas Söderlund <niklas.soderlund@corigine.com>
Signed-off-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220315102948.466436-1-niklas.soderlund@corigine.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
samples/bpf/xdpsock_user.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
index aa50864e4415..9f3446af50ce 100644
--- a/samples/bpf/xdpsock_user.c
+++ b/samples/bpf/xdpsock_user.c
@@ -1984,15 +1984,15 @@ int main(int argc, char **argv)

setlocale(LC_ALL, "");

+ prev_time = get_nsecs();
+ start_time = prev_time;
+
if (!opt_quiet) {
ret = pthread_create(&pt, NULL, poller, NULL);
if (ret)
exit_with_error(ret);
}

- prev_time = get_nsecs();
- start_time = prev_time;
-
/* Configure sched priority for better wake-up accuracy */
memset(&schparam, 0, sizeof(schparam));
schparam.sched_priority = opt_schprio;
--
2.34.1