netdev - Re: [PATCH RFC] r8152: Ensure that napi

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Message-ID: <20210514123838.10d78c35@kicinski-fedora-PC1C0HJN>
Date:   Fri, 14 May 2021 12:38:38 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-usb@...r.kernel.org, netdev@...r.kernel.org,
        Michal Svec <msvec@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Hayes Wang <hayeswang@...ltek.com>,
        Thierry Reding <treding@...dia.com>,
        Lee Jones <lee.jones@...aro.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH RFC] r8152: Ensure that napi_schedule() is handled

On Fri, 14 May 2021 12:17:19 +0200 Thomas Gleixner wrote:
> The driver invokes napi_schedule() in several places from task
> context. napi_schedule() raises the NET_RX softirq bit and relies on the
> calling context to ensure that the softirq is handled. That's usually on
> return from interrupt or on the outermost local_bh_enable().
> 
> But that's not the case here which causes the soft interrupt handling to be
> delayed to the next interrupt or local_bh_enable(). If the task in which
> context this is invoked is the last runnable task on a CPU and the CPU goes
> idle before an interrupt arrives or a local_bh_disable/enable() pair
> handles the pending soft interrupt then the NOHZ idle code emits the
> following warning.
> 
>   NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #08!!!
> 
> Prevent this by wrapping the napi_schedule() invocation from task context
> into a local_bh_disable/enable() pair.

I should have read through my inbox before replying :)

I'd go for switching to raise_softirq_irqoff() in ____napi_schedule()...
why not?