netdev - Re: [PATCH net] r8169: fix operation under forced interrupt threading

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Message-ID: <877drabmoq.fsf@depni.sinp.msu.ru>
Date:   Wed, 28 Oct 2020 14:43:33 +0300
From:   Serge Belyshev <belyshev@...ni.sinp.msu.ru>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] r8169: fix operation under forced interrupt threading


> For several network drivers it was reported that using
> __napi_schedule_irqoff() is unsafe with forced threading. One way to
> fix this is switching back to __napi_schedule, but then we lose the
> benefit of the irqoff version in general. As stated by Eric it doesn't
> make sense to make the minimal hard irq handlers in drivers using NAPI
> a thread. Therefore ensure that the hard irq handler is never
> thread-ified.
>
> Fixes: 9a899a35b0d6 ("r8169: switch to napi_schedule_irqoff")
> Link: https://lkml.org/lkml/2020/10/18/19
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
>  drivers/net/ethernet/realtek/r8169_main.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
> index 7d366b036..3b6ddc706 100644
> --- a/drivers/net/ethernet/realtek/r8169_main.c
> +++ b/drivers/net/ethernet/realtek/r8169_main.c
...

Hi!  This patch actually breaks r8169 with threadirqs on an old box
where it was working before:

[    0.000000] DMI: Gigabyte Technology Co., Ltd. GA-MA790FX-DQ6/GA-MA790FX-DQ6, BIOS F7g 07/19/2010
...
[    1.072676] r8169 0000:02:00.0 eth0: RTL8168b/8111b, 00:1a:4d:5d:6b:c3, XID 380, IRQ 18
...
[    8.850099] genirq: Flags mismatch irq 18. 00010080 (eth0) vs. 00002080 (ahci[0000:05:00.0])

(error is reported to userspace, interface failed to bring up).
Reverting the patch fixes the problem.