netdev - Re: [PATCH v6] netpoll: protect napi_poll and poll_controller during dev

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Date:	Wed, 06 Feb 2013 15:45:29 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	nhorman@...driver.com
Cc:	netdev@...r.kernel.org, ivecera@...hat.com,
	bhutchings@...arflare.com, romieu@...zoreil.com,
	eric.dumazet@...il.com
Subject: Re: [PATCH v6] netpoll: protect napi_poll and poll_controller
 during dev_[open|close]

From: Neil Horman <nhorman@...driver.com>
Date: Tue,  5 Feb 2013 13:05:43 -0500

> Ivan Vercera was recently backporting commit
> 9c13cb8bb477a83b9a3c9e5a5478a4e21294a760 to a RHEL kernel, and I noticed that,
> while this patch protects the tg3 driver from having its ndo_poll_controller
> routine called during device initalization, it does nothing for the driver
> during shutdown. I.e. it would be entirely possible to have the
> ndo_poll_controller method (or subsequently the ndo_poll) routine called for a
> driver in the netpoll path on CPU A while in parallel on CPU B, the ndo_close or
> ndo_open routine could be called.  Given that the two latter routines tend to
> initizlize and free many data structures that the former two rely on, the result
> can easily be data corruption or various other crashes.  Furthermore, it seems
> that this is potentially a problem with all net drivers that support netpoll,
> and so this should ideally be fixed in a common path.
> 
> As Ben H Pointed out to me, we can't preform dev_open/dev_close in atomic
> context, so I've come up with this solution.  We can use a mutex to sleep in
> open/close paths and just do a mutex_trylock in the napi poll path and abandon
> the poll attempt if we're locked, as we'll just retry the poll on the next send
> anyway.
> 
> I've tested this here by flooding netconsole with messages on a system whos nic
> driver I modfied to periodically return NETDEV_TX_BUSY, so that the netpoll tx
> workqueue would be forced to send frames and poll the device.  While this was
> going on I rapidly ifdown/up'ed the interface and watched for any problems.
> I've not found any.
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>

Applied to net-next, thanks Neil.
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