netdev - Re: [PATCH 1/2] ipv6: do not hold route table lock when send ndisc probe

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Date:	Fri, 24 Aug 2012 17:15:24 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Debabrata Banerjee <dbavatar@...il.com>, netdev@...r.kernel.org,
	"Banerjee, Debabrata" <dbanerje@...mai.com>,
	"David S. Miller" <davem@...emloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH 1/2] ipv6: do not hold route table lock when send ndisc
 probe

On Thu, 2012-08-23 at 18:10 +0200, Eric Dumazet wrote:
> On Tue, 2012-08-21 at 11:44 +0800, Cong Wang wrote:
> > Hi, Debabrata,
> > 
> > Could you help to test the attached patch below?
> > 
> > Thanks!
> > 
> 
> Hard to comment on your patch since its not inlined.
> 
> +               nw = kmalloc(sizeof(*nw), GFP_ATOMIC);
> +               if (nw) {
> +                       memcpy(&nw->target, &neigh->primary_key, sizeof(struct in6_addr));
> +                       addrconf_addr_solict_mult(&nw->target, &nw->mcaddr);
> +                       nw->dev = rt->dst.dev;
> +                       INIT_WORK(&nw->work, queue_ndisc);
> +                       schedule_work(&nw->work);
> +               }
> 
> You cant do that without taking extra reference on dev,
> and release it in queue_ndisc()
> 
> This also will add interesting side effects at device dismantle.
> 

Right... If we call dev_hold() in the work, it is possible that the work
is still not scheduled to running when we unregister the device. What's
more, we can't flush work here as we are holding a read lock.

Hmm.


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