netdev - Re: Q: what protects dev->napi

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Date:	Sat, 25 Aug 2012 14:08:42 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org,
	Sylvain Munaut <s.munaut@...tever-company.com>,
	David Miller <davem@...emloft.net>
Subject: Re: Q: what protects dev->napi_list?

On Fri, 2012-08-24 at 13:29 +0200, Eric Dumazet wrote:
> On Fri, 2012-08-24 at 18:39 +0800, Cong Wang wrote:
> > 
> > Yeah, but bnx2 driver calls it at other time too, for example
> > bnx2_change_ring_size() which in turn could be called by
> > bnx2_set_channels().
> 
> Then at this point, device is stopped, or should be.
> 

But poll_napi() is still iterating the dev->napi_list, could anyone
stops it?

IOW, the following race condition may happen:

static void poll_napi(struct net_device *dev)
{               
        struct napi_struct *napi;
        int budget = 16;
                
        WARN_ON_ONCE(!irqs_disabled());
                
        list_for_each_entry(napi, &dev->napi_list, dev_list) {
                local_irq_enable();

				//<-- Another process may call
				//bnx2_change_ring_size() to del
				//napi from dev, on other CPU.

                local_irq_disable();
        }
}


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