From mboxrd@z Thu Jan  1 00:00:00 1970
From: Patrick McHardy <kaber@trash.net>
Subject: Re: [PATCH][NET_SCHED] sch_api: fix qdisc_tree_decrease_qlen() loop
Date: Mon, 14 Apr 2008 22:28:52 +0200
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References: <47FFAFFA.7070802@superclick.com> <20080413121031.GA5211@ami.dom.local> <20080414202605.GA6164@ami.dom.local>
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Cc: David Miller <davem@davemloft.net>,
	Enrico Demarin <enrico@superclick.com>, netdev@vger.kernel.org
To: Jarek Poplawski <jarkao2@gmail.com>
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Jarek Poplawski wrote:
> [NET_SCHED] sch_api: fix qdisc_tree_decrease_qlen() loop
>
> TC_H_MAJ(parentid) for root classes is the same as for ingress, and if
> ingress qdisc is created qdisc_lookup() returns its pointer (without
> ingress NULL is returned). After this all qdisc_lookups give the same,
> and we get endless loop. (I don't know how this could hide for so
> long - it should trigger with every leaf class deleted if it's qdisc
> isn't empty.)
>
> After this fix qdisc_lookup() is omitted both for ingress and root
> parents, but looking for root is only wasting a little time here...
> Many thanks to Enrico Demarin for finding a test for catching this
> bug, which probably bothered quite a lot of admins.
>   

Good catch, I agree that this is the reason for sure.