netdev - Re: BUG: scheduling while atomic: ifconfig/0x00000002/4170

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Message-Id: <200709071801.34909.mb@bu3sch.de>
Date:	Fri, 7 Sep 2007 18:01:34 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	paulmck@...ux.vnet.ibm.com,
	Herbert Xu <herbert@...dor.apana.org.au>, satyam@...radead.org,
	flo@...822.org, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, linux-wireless@...r.kernel.org,
	michal.k.k.piotrowski@...il.com,
	ipw3945-devel@...ts.sourceforge.net, yi.zhu@...el.com,
	flamingice@...rmilk.net
Subject: Re: BUG: scheduling while atomic: ifconfig/0x00000002/4170

On Friday 07 September 2007, Johannes Berg wrote:
> On Thu, 2007-09-06 at 08:46 -0700, Paul E. McKenney wrote:
> 
> > Looks good to me from an RCU viewpoint.  I cannot claim familiarity with
> > this code.  I therefore especially like the indications of where RTNL
> > is held and not!!!
> 
> :)
> 
> > Some questions below based on a quick scan.  And a global question:
> > should the comments about RTNL being held be replaced by ASSERT_RTNL()?
> 
> I don't like ASSERT_RTNL() much because it actually tries to lock it.
> I'd be much happer if it was WARN_ON(!mutex_locked(&rtnl_mutex)) or
> something equivalent.

What's the problem with trying to lock it?
In the paths where you insert this assertion, you will be locked.
So the trylock will fail and not cause any blocking or something else.
It's basically not more expensive than your mutex_locked test.
And the !mutex_locked test might not work on UP (Not sure, about
the current implementation.)
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