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

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Message-ID: <1359580042.2789.53.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Wed, 30 Jan 2013 21:07:22 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	<netdev@...r.kernel.org>, Ivan Vecera <ivecera@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] netpoll: protect napi_poll and poll_controller during
 dev_[open|close]

On Wed, 2013-01-30 at 15:44 -0500, Neil Horman wrote:
> 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.
> 
> Fix it by creating a spinlock in the netpoll_info structure, and holding it on
> netpoll_poll_dev, and in dev_close and dev_open.  That will prevent the driver
> from getting torn down while we're using it in the netpoll path
> 
> I've done some testing on this, flooding a netconsole enabled system with
> messages and ifup/downing the interface. No problems observed
> 
> Signed-off-by: Neil Horman <nhorman@...driver.com>
> CC: Ivan Vecera <ivecera@...hat.com>
> CC: "David S. Miller" <davem@...emloft.net>
> ---
>  include/linux/netpoll.h |  1 +
>  net/core/dev.c          | 16 ++++++++++++++++
>  net/core/netpoll.c      |  3 +++
>  3 files changed, 20 insertions(+)
> 
> diff --git a/include/linux/netpoll.h b/include/linux/netpoll.h
> index f54c3bb..bb1d364 100644
> --- a/include/linux/netpoll.h
> +++ b/include/linux/netpoll.h
> @@ -40,6 +40,7 @@ struct netpoll_info {
>  
>  	int rx_flags;
>  	spinlock_t rx_lock;
> +	spinlock_t napi_lock;
>  	struct list_head rx_np; /* netpolls that registered an rx_hook */
>  
>  	struct sk_buff_head neigh_tx; /* list of neigh requests to reply to */
> diff --git a/net/core/dev.c b/net/core/dev.c
> index a87bc74..18f85e1 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1307,11 +1307,19 @@ static int __dev_open(struct net_device *dev)
>  int dev_open(struct net_device *dev)
>  {
>  	int ret;
> +	struct netpoll_info *ni;
>  
>  	if (dev->flags & IFF_UP)
>  		return 0;
>  
> +	rcu_read_lock();
> +	ni = rcu_dereference(dev->npinfo);
> +	if (ni)
> +		spin_lock(&ni->napi_lock);
>  	ret = __dev_open(dev);
> +	if (ni)
> +		spin_unlock(&ni->napi_lock);
[...]

No, you can't call ndo_open and ndo_stop in atomic context.

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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