Re: [Patch] bonding: fix netpoll in active-backup mode

[Cong Wang]

ä 2011å03æ08æ 12:15, Cong Wang åé:
> ä 2011å03æ08æ 02:50, Neil Horman åé:
> > On Mon, Mar 07, 2011 at 10:11:50PM +0800, Amerigo Wang wrote:
> > > netconsole doesn't work in active-backup mode, because we don't do anything
> > > for nic failover in active-backup mode. This patch fixes the problem by:
> > >
> > > 1) make slave_enable_netpoll() and slave_disable_netpoll() callable in softirq
> > > context, that is, moving code after synchronize_rcu_bh() into call_rcu_bh()
> > > callback function, teaching kzalloc() to use GFP_ATOMIC.
> > >
> > > 2) disable netpoll on old slave and enable netpoll on the new slave.
> > >
> > > Tested by ifdown the current active slave and ifup it again for several times,
> > > netconsole works well.
> > >
> > > Signed-off-by: WANG Cong<amwang@xxxxxxxxxx>
> > I may be missing soething but this seems way over-complicated to me. I presume
> > the problem is that in active backup mode a failover results in the new active
> > slave not having netpoll setup on it? If thats the case, why not just setup
> > netpoll on all slaves when ndo_netpoll_setup is called on the bonding interface?
> > I don't see anything immeidately catastrophic that would happen as a result.
>
>
> But we still need to clean up the netpoll on the failing slave, which still
> needs to call slave_disable_netpoll() in monitor code, I see no big differences
> with the solution I take.
>
>
> > And then you wouldn't have to worry about disabling/enabling anything on a
> > failover (or during a panic for that matter). As for the rcu bits? Why are
> > they needed? One would presume that wouldn't (or at least shouldn't) be able to
> > teardown our netpoll setup until such time as all the pending frames for that
> > netpoll client have been transmitted. If we're not blocknig on that RCU isn't
> > really going to help. Seems like the proper fix is take a reference to the
> > appropriate npinfo struct in netpoll_send_skb, and drop it from the skbs
> > destructor or some such.
>
> I saw a "scheduling while in atomic" warning without touching the rcu bits.

Hmm, I was wrong, this warning is misleading, I think the root cause is that
I call slave_disable_netpoll() with write_lock_bh() held...

Will update the patch soon...
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