netdev - Re: [PATCH] ethernet: mvneta: Support netpoll

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Date:	Tue, 29 Mar 2016 23:09:30 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ezequiel@...guardiasur.com.ar
Cc:	thomas.petazzoni@...e-electrons.com, netdev@...r.kernel.org
Subject: Re: [PATCH] ethernet: mvneta: Support netpoll

From: Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Date: Mon, 28 Mar 2016 17:41:18 -0300

> +/* Polled functionality used by netconsole and others in non interrupt mode */
> +static void mvneta_poll_controller(struct net_device *dev)
> +{
> +	struct mvneta_port *pp = netdev_priv(dev);
> +
> +	on_each_cpu(mvneta_percpu_poll_controller, pp, false);
> +}

This doesn't work.

netpoll may be invoked from any context whatsoever, even hardware
interrupt handlers or contexts where cpu interrupts are disabled.

smp_call_function() and thus on_each_cpu() may not be called with
disabled interrupts or from a hardware interrupt handler or from
a bottom half handler, all of which are valid situations where
netpoll may occur since printk's can occur anywhere.