netdev - Re: [Bug, PATCH and another Bug] Was: Fix refcounting problem with netif_rx

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Message-Id: <20070920.111228.76772435.davem@davemloft.net>
Date:	Thu, 20 Sep 2007 11:12:28 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	krkumar2@...ibm.com
Cc:	general@...ts.openfabrics.org, netdev@...r.kernel.org,
	rdreier@...co.com
Subject: Re: [Bug, PATCH and another Bug] Was: Fix refcounting problem with
 netif_rx_reschedule()

From: Krishna Kumar2 <krkumar2@...ibm.com>
Date: Thu, 20 Sep 2007 10:48:15 +0530

> About the "list deletion occurs", isn't the race I mentioned still present?
> If done < budget, the driver does netif_rx_complete (at which time some
> other cpu can add this NAPI to their list). But the first cpu might do some more
> actions on the napi, like ipoib_poll() calls request_notify_cq(priv->cq),
> when other cpu might have started using this napi.
> 
> (net_rx_action's 'list_move' however will not execute since work != weight)

It is the driver's responsibility to adhere to the fact that once
netif_rx_complete() is called, the driver is explicitly relinquishing
ownership of the NAPI state.

It therefore must not access that NAPI state until it has successfully
acquired the NAPI_STATE_SCHED bit atomically, via a sched or resched.

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