netdev - Re: [BUG] RTNL and flush_scheduled

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Message-ID: <20070216103115.517f1a4c@freekitty>
Date:	Fri, 16 Feb 2007 10:31:15 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Ben Greear <greearb@...delatech.com>
Cc:	Jarek Poplawski <jarkao2@...pl>,
	Francois Romieu <romieu@...zoreil.com>, netdev@...r.kernel.org,
	Kyle Lucke <klucke@...ibm.com>,
	Raghavendra Koushik <raghavendra.koushik@...erion.com>,
	Al Viro <viro@....linux.org.uk>
Subject: Re: [BUG] RTNL and flush_scheduled_work deadlocks

On Thu, 15 Feb 2007 23:40:32 -0800
Ben Greear <greearb@...delatech.com> wrote:

> Jarek Poplawski wrote:
> > On 14-02-2007 22:27, Stephen Hemminger wrote:
> >   
> >> Ben found this but the problem seems pretty widespread.
> >>
> >> The following places are subject to deadlock between flush_scheduled_work
> >> and the RTNL mutex. What can happen is that a work queue routine (like
> >> bridge port_carrier_check) is waiting forever for RTNL, and the driver
> >> routine has called flush_scheduled_work with RTNL held and is waiting
> >> for the work queue to clear.
> >>
> >> Several other places have comments like: "can't call flush_scheduled_work
> >> here or it will deadlock". Most of the problem places are in device close
> >> routine. My recommendation would be to add a check for device netif_running in
> >> what ever work routine is used, and move the flush_scheduled_work to the
> >> remove routine.
> >>
> >> 8139too.c: rtl8139_close --> rtl8139_stop_thread
> >> r8169.c:   rtl8169_down
> >> cassini.c: cas_change_mtu
> >> iseries_veth.c: veth_stop_connection
> >> s2io.c: s2io_close
> >> sis190.c: sis190_down
> >>
> >>     
> >
> > There is probably more than this...
> >   
> 
> Maybe there should be something like an ASSERT_NOT_RTNL() in the 
> flush_scheduled_work()
> method?  If it's performance criticial, #ifdef it out if we're not 
> debugging locks?
> 

You can't safely add a check like that. What if another cpu had acquired
RTNL and was unrelated.


-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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