From: Eric Dumazet <eric.dumazet@gmail.com>
To: Cong Wang <amwang@redhat.com>
Cc: netdev@vger.kernel.org,
Sylvain Munaut <s.munaut@whatever-company.com>,
David Miller <davem@davemloft.net>
Subject: Re: Q: what protects dev->napi_list?
Date: Fri, 24 Aug 2012 12:12:22 +0200 [thread overview]
Message-ID: <1345803142.29722.20.camel@edumazet-glaptop> (raw)
In-Reply-To: <1345801604.11584.24.camel@cr0>
On Fri, 2012-08-24 at 17:46 +0800, Cong Wang wrote:
> Hi,
>
> Sylvain reported a netpoll CPU stall
> http://marc.info/?l=linux-netdev&m=134563282530588&w=2
>
> I tried to provide some fix for it:
> http://marc.info/?l=linux-netdev&m=134571069921429&w=2
>
> When reviewing that code, I noticed a problem, it seems dev->napi_list
> is not protected by any lock? What if the device driver calls
> netif_napi_del() meanwhile we are iterating &dev->napi_list in
> poll_napi()? It seems netif_napi_del()/netif_napi_add() are usually
> called with the RTNL lock held during driver init/uninit, but again
> poll_napi() doesn't have RTNL lock.
>
Of course poll_napi() cant try to get RTNL (its a mutex by the way)
There are no problems, since :
netif_napi_add() is called at device open time (before napi_poll() can
use it)
netif_napi_del() at device dismantle time (after making sure napi_poll()
wont use the device again)
next prev parent reply other threads:[~2012-08-24 10:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-24 9:46 Q: what protects dev->napi_list? Cong Wang
2012-08-24 10:12 ` Eric Dumazet [this message]
2012-08-24 10:39 ` Cong Wang
2012-08-24 11:29 ` Eric Dumazet
2012-08-25 6:08 ` Cong Wang
2012-08-25 6:49 ` Eric Dumazet
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