Re: [PATCH v2 bpf] selftests/bpf: Wait for receive in cg_storage_multi test

[Martin KaFai Lau <martin.lau@linux.dev>]

On 4/5/23 12:33 PM, YiFei Zhu wrote:
> In some cases the loopback latency might be large enough, causing
> the assertion on invocations to be run before ingress prog getting
> executed. The assertion would fail and the test would flake.
> 
> This can be reliably reproduced by arbitrarily increasing the
> loopback latency (thanks to [1]):
>    tc qdisc add dev lo root handle 1: htb default 12
>    tc class add dev lo parent 1:1 classid 1:12 htb rate 20kbps ceil 20kbps
>    tc qdisc add dev lo parent 1:12 netem delay 100ms
> 
> Fix this by waiting on the receive end, instead of instantly
> returning to the assert. The call to read() will wait for the
> default SO_RCVTIMEO timeout of 3 seconds provided by
> start_server().
> 
> [1] https://gist.github.com/kstevens715/4598301
> 
> Reported-by: Martin KaFai Lau <martin.lau@linux.dev>
> Link: https://lore.kernel.org/bpf/9c5c8b7e-1d89-a3af-5400-14fde81f4429@linux.dev/
> Fixes: 3573f384014f ("selftests/bpf: Test CGROUP_STORAGE behavior on shared egress + ingress")
> Signed-off-by: YiFei Zhu <zhuyifei@google.com>
> ---
> v1 -> v2:
> - Changed from a call to poll() to a call to read() (Martin)

Thanks for the fix. Added "Acked-by: Stanislav Fomichev <sdf@google.com>" and 
applied.