netdev - Re: [patchlet] r8169: fix napi_schedule_irqoff() called with irqs enabled warning

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Date:   Fri, 16 Oct 2020 20:19:36 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Mike Galbraith <efault@....de>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>
Subject: Re: [patchlet] r8169: fix napi_schedule_irqoff() called with irqs
 enabled warning

On Fri, Oct 16, 2020 at 07:11:22PM +0200, Mike Galbraith wrote:
> Yeah, it's a straight up correctness issue as it sits.

Yeah, tell me about it, you don't even want to know what it looks like
when the local_softirq_pending_ref percpu mask gets corrupted. The
symptom will be that random syscalls, like clock_nanosleep, will make
user processes hang in the kernel, because their timers will appear to
never expire. You'll also see negative expiry times in /proc/timer_list.
Eventually the entire system dies. All of that, reproducible with a
simple flood ping, given enough time.  Ask me how I come to know....
The 215602a8d212 ("enetc: use napi_schedule to be compatible with
PREEMPT_RT") commit is from before the lockdep warning came to be.