netdev - Re: [PATCH] net: deadlock during net device unregistration

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Date:	Sun, 5 Oct 2008 09:28:23 +0200
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	Benjamin Thery <benjamin.thery@...l.net>, davem@...emloft.net,
	netdev@...r.kernel.org, dlezcano@...ibm.com
Subject: Re: [PATCH] net: deadlock during net device unregistration

On Sun, 5 Oct 2008 09:12:38 +0200
Jarek Poplawski <jarkao2@...il.com> wrote:

> On Sun, Oct 05, 2008 at 02:56:48PM +0800, Herbert Xu wrote:
> > On Sun, Oct 05, 2008 at 08:55:10AM +0200, Jarek Poplawski wrote:
> > >
> > > > -	/* Not safe to do outside the semaphore.  We must not return
> > > > -	 * until all unregister events invoked by the local processor
> > > > -	 * have been completed (either by this todo run, or one on
> > > > -	 * another cpu).
> > > > -	 */
> > > 
> > > I think, it's about not to let others run this for devices unregistered
> > > within later rtnl_locks before completing previous tasks. So, it would
> > > be nice to have some comment why it's not necessary anymore.
> > 
> > Where did you get that idea?
> 
> Just reading this code (plus the comment). Why would anybody bother 
> with something so complex like this if something like your idea is
> rather straightforward? But, needed or not, my point is it would be
> nice to comment that this patch changes this behavior btw.

I think there were issues with unregister triggering hotplug udev
events, but that may have been long ago when rtnl_lock was
a semaphore not a mutex.
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