netdev - Re: [PATCH net] net/sched: Fix use of wild pointer in mq_destroy() when qdisc

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Date:	Fri, 24 Oct 2014 20:14:19 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Cong Wang <cwang@...pensource.com>
Cc:	John Fastabend <john.fastabend@...il.com>, wang.bo116@....com.cn,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, cui.yunfeng@....com.cn
Subject: Re: [PATCH net] net/sched: Fix use of wild pointer in mq_destroy()
 when qdisc_alloc fail

On Fri, Oct 24, 2014 at 11:13:56AM -0700, Cong Wang wrote:
> On Fri, Oct 24, 2014 at 10:49 AM, John Fastabend
> <john.fastabend@...il.com> wrote:
> >
> > Patch looks fine, another way to fix this would be drop the
> > mq_destroy() call in the error path. I'm not convinced one
> > is any better than the other but maybe some other folks have
> > opinions, it seems a bit wrong to call mq_destroy twice so in
> > that sense it may be a bit nicer to drop the mq_destroy().
> 
> Dropping mq_destroy() in error path is indeed better,
> because upper layer does cleanup intentionally.
> Look at what other qdisc's do. :)

I would argue that the qdisc_destroy() call in qdisc_create_dflt()
is wrong, it should instead free the qdisc and release the module
reference manually as done in qdisc_create().

qdisc_destroy() should only be called for fully initialized qdiscs.
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