netdev - Re: ping -I eth1 ....

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Date:	Wed, 17 Nov 2010 11:23:32 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
Cc:	netdev@...r.kernel.org, Thomas Graf <tgraf@...radead.org>
Subject: Re: ping -I eth1 ....

Le mercredi 17 novembre 2010 à 11:09 +0100, Joakim Tjernlund a écrit :
> Eric Dumazet <eric.dumazet@...il.com> wrote on 2010/11/17 10:51:07:
> >
> > Le mercredi 17 novembre 2010 à 10:29 +0100, Joakim Tjernlund a écrit :
> > > Joakim Tjernlund/Transmode wrote on 2010/11/09 20:33:37:
> > > >
> > > > Joakim Tjernlund/Transmode wrote on 2010/11/06 10:42:46:
> > > > > Thomas Graf <tgr@...radead.org> wrote on 2010/11/05 21:31:50:
> > > > > >
> > > > > > On Fri, Nov 05, 2010 at 04:54:18PM +0100, Joakim Tjernlund wrote:
> > > > > > > Eric Dumazet <eric.dumazet@...il.com> wrote on 2010/11/05 16:06:54:
> > > > > > > >
> > > > > > > > > Hopefully most of that is legacy or just plain wrong? Unless
> > > > > > > > > someone can say why only test IFF_UP one should consider changing them.
> > > > > > > > >
> > > > > > > >
> > > > > > > > Most of the places are hot path.
> > > > > > > >
> > > > > > > > You dont want to replace one test by four tests.
> > > > > > > >
> > > > > > > > _This_ would be wrong :)
> > > > > > >
> > > > > > > Wrong is wrong, even if it is in the hot path :)
> > > > > > > Perhaps it is time define and internal IFF_OPERATIONAL flag
> > > > > > > which is the sum of IFF_UP, IFF_RUNNING etc.? Tht
> > > > > > > way you still get one test in the hot path and can abstract
> > > > > > > what defines an operational link.
> > > > > >
> > > > > > You definitely don't want to have your send() call fail simply because
> > > > > > the carrier was off for a few msec or the routing daemon has put a link
> > > > > > down temporarly. Also, the outgoing interface looked up at routing
> > > > > > decision is not necessarly the interface used for sending in the end.
> > > > > > The packet may get mangled and rerouted by netfilter or tc on the way.
> > > > >
> > > > > But do you handle the case when the link is non operational for a long time?
> > > > >
> > > > > >
> > > > > > Personally I'm even ok with the current behaviour of sendto() while the
> > > > > > socket is bound to an interface but if we choose to return an error
> > > > > > if the interface is down we might as well do so based on the operational
> > > > > > status.
> > >
> > > > > Perhaps there is a better way. This all started when pppd hung because
> > > > > of ping -I <ppp interface>, then someone pulled the cable for the on the link.
> > > > >
> > > > > This is a strace where we have two ping -I,
> > > > > ping -I p1-2-1-2-2 .. and ping -I p1-2-3-2-4 ..
> > > > > Notice how pppd hangs for a long time in PPPIOCDETACH
> > > > > As far as I can tell this is due to ping -I has claimed the ppp interfaces
> > > > > and doesn't noticed that the link is down. Ideally ping should receive
> > > > > a ENODEV as soon as pppd calls PPPIOCDETACH.
> > > > >
> > > > >    0.000908 write(0, "Connection terminated.\n", 23) = 23
> > > > >      0.000481 gettimeofday({1288952770, 566048}, NULL) = 0
> > > > >      0.001553 ioctl(7, PPPIOCDETACH
> > > > > Message from syslogd@...zil at Fri Nov  5 11:26:20 2010 ...
> > > > > Brazil kernel: unregister_netdevice: waiting for p1-2-1-2-2 to become free. Usage count = 3
> > > > > Message from syslogd@...zil at Fri Nov  5 11:26:20 2010 ...
> > > > > Brazil kernel: unregister_netdevice: waiting for p1-2-3-2-4 to become free. Usage count = 3
> > > > > Message from syslogd@...zil at Fri Nov  5 11:26:51 2010 ...
> > > > > Brazil last message repeated 3 times
> > > > > , 0xbfbc3398) = 0
> > > > >     66.559216 connect(9, {sa_family=AF_PPPOX, sa_data="\0\0\0\0\0\0\0\252\273\314\335\356hd"}, 30) = 0
> > > > >      0.000693 close(10)                 = 0
> > > > >      0.000449 close(7)                  = 0
> > > > >      0.009801 close(9)                  = 0
> > > >
> > > > Any comment on this last strace? It is expected that ping -I should
> > > > hold pppd hostage?
> > > >
> > >
> > > Ping?
> > >
> >
> > I thought I posted a patch, is there something else ?
> 
> yes, I wondered about the above strace and if it is expected that ping -I
> should hold pppd hostage? Should not ping receive a ENODEV as soon as
> pppd detaches an interface?
> 
> >
> > Could you please test with latest net-next-2.6 and following patch ?
> 
> I tested the first patch you sent and that one worked well. I can try
> again on 2.6.35( our boards takes a while to move forward)?

Well, in this case, apply commit : 

332dd96f7ac15e937088fe11f15cfe0210e8edd1

(net/dst: dst_dev_event() called after other notifiers)

http://git2.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=332dd96f7ac15e937088fe11f15cfe0210e8edd1



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