netdev - Re: [PATCH net] net/mlx4_en: mlx4_en_netpoll shouldn't call napi

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Date:	Mon, 29 Sep 2014 13:47:04 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	amirv@...lanox.com
Cc:	idos@...lanox.com, netdev@...r.kernel.org, yevgenyp@...lanox.com,
	ogerlitz@...lanox.com
Subject: Re: [PATCH net] net/mlx4_en: mlx4_en_netpoll shouldn't call
 napi_schedule when port is down

From: Amir Vadai <amirv@...lanox.com>
Date: Mon, 29 Sep 2014 14:04:55 +0300

> From: Ido Shamay <idos@...lanox.com>
> 
> mlx4_en_netpoll, which is mlx4_en ndo_poll_controller callback,
> might be called when port is down, causing a napi_schedule when
> napi->poll callback in NULL. mutex_trylock is needed to acquire
> the port_state lock, since other threads may grab it and stop
> the port while we are in napi scheduling. Using trylock since in atomic
> context.
> 
> Signed-off-by: Ido Shamay <idos@...lanox.com>
> Signed-off-by: Amir Vadai <amirv@...lanox.com>

I don't think netpoll should 'variably succeed' on poll controller's
ability to immediately take a trylock.

You need to find a way to make this code always process the queues
when it is called, the approach you are taking here is not a correct.

If you've designed things in such a way that the locking here is
difficult, that's unfortunate but you still have to make this
function behave properly.
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