netdev - Re: [PATCH net-next 1/2] selftests: net-drv: exercise queue stats when the device is down

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Message-ID: <20240729185801.7013ecd3@kernel.org>
Date: Mon, 29 Jul 2024 18:58:01 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Stanislav Fomichev <sdf@...ichev.me>
Cc: netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, Shuah Khan <shuah@...nel.org>, Joe Damato
 <jdamato@...tly.com>, Petr Machata <petrm@...dia.com>,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next 1/2] selftests: net-drv: exercise queue stats
 when the device is down

On Mon, 29 Jul 2024 15:10:41 -0700 Stanislav Fomichev wrote:
> Verify that total device stats don't decrease after it has been turned down.
> Also make sure the device doesn't crash when we access per-queue stats
> when it's down (in case it tries to access some pointers that are NULL).
> 
> KTAP version 1
> 1..5
> ok 1 stats.check_pause
> ok 2 stats.check_fec
> ok 3 stats.pkt_byte_sum
> ok 4 stats.qstat_by_ifindex
> ok 5 stats.check_down
> \# Totals: pass:5 fail:0 xfail:0 xpass:0 skip:0 error:0

nit: may be personal preference but if you indent by 2 spaces
     that will neutralize the # as well

> +def check_down(cfg) -> None:
> +    try:
> +        qstat = netfam.qstats_get({"ifindex": cfg.ifindex}, dump=True)
> +    except NlError as e:
> +        if e.error == 95:
> +            raise KsftSkipEx("qstats not supported by the device")
> +        raise
> +
> +    ip(f"link set dev {cfg.dev['ifname']} down")
> +
> +    try:

The rest of this test predates defer() but I think it may be cleaner:

	ip(f"link set dev {cfg.dev['ifname']} down")
	defer(ip, f"link set dev {cfg.dev['ifname']} up")

then you don't need to try/finally.

> +        qstat = qstat[0]
> +        qstat2 = netfam.qstats_get({"ifindex": cfg.ifindex}, dump=True)[0]
> +        for k, v in qstat.items():
> +            if k not in qstat2:
> +                # skip the stats that are not globally preserved
> +                continue

I think we should fail if stats disappear. I can't think of a legit
reason for that to happen.

> +            if qstat2[k] < qstat[k]:
> +                raise Exception(f"{k} ({qstat2[k]}) should be preserved but has lower value ({qstat[k]}) when the device is down")

	ksft_ge(qstat2[k], qstat[k], comment=k)
?

> +
> +        # exercise per-queue API to make sure that "device down" state
> +        # is handled correctly and doesn't crash
> +        netfam.qstats_get({"ifindex": cfg.ifindex, "scope": "queue"}, dump=True)
> +    finally:
> +        ip(f"link set dev {cfg.dev['ifname']} up")
> +
> +
>  def main() -> None:
>      with NetDrvEnv(__file__) as cfg:
> -        ksft_run([check_pause, check_fec, pkt_byte_sum, qstat_by_ifindex],
> +        ksft_run([check_pause, check_fec, pkt_byte_sum, qstat_by_ifindex,
> +                  check_down],
>                   args=(cfg, ))
>      ksft_exit()
>