netdev - Re: [Patch net 2/2] net_sched: always call ->destroy when ->init() fails

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Date:	Sat, 25 Oct 2014 01:36:45 +0100
From:	Patrick McHardy <kaber@...sh.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org,
	davem@...emloft.net, Wang Bo <wang.bo116@....com.cn>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Terry Lam <vtlam@...gle.com>
Subject: Re: [Patch net 2/2] net_sched: always call ->destroy when ->init()
 fails

On Fri, Oct 24, 2014 at 05:14:13PM -0700, Eric Dumazet wrote:
> On Fri, 2014-10-24 at 16:55 -0700, Cong Wang wrote:
> > In qdisc_create(), when ->init() exists and it fails, we should
> > call ->destroy() to clean up the potentially partially initialized
> > qdisc's. This will also make the ->init() implementation easier.
> > 
> 
> Why is this patch needed ?
> 
> You are adding bugs, its not clear what bug you are fixing.
> 
> I really do not like the idea of ->init() relying on a ->destroy() to
> cleanup a failed ->init().
> 
> This is not what most management functions do in our stack.
> 
> I very much prefer that a function returning an error has no side
> effect, like if it hadnt be called at all.

Absolutely.

Again, the correct fix is to make qdisc_create_dflt() not call
qdisc_destroy() but clean up the qdisc manually as done in
qdisc_create().
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