netdev - Re: [Patch net] netns: avoid allocating idr when dumping info

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Message-ID: <1425024069.5130.10.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 27 Feb 2015 00:01:09 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: Re: [Patch net] netns: avoid allocating idr when dumping info

On Thu, 2015-02-26 at 22:32 -0800, Cong Wang wrote:
> We can allocate the peer netns id when creating the link
> instead of when dumping the link.
> 
> This fixes the following kernel warning:
> 
>  ===============================
>  [ INFO: suspicious RCU usage. ]
>  3.19.0+ #805 Tainted: G        W
>  -------------------------------
>  include/linux/rcupdate.h:538 Illegal context switch in RCU read-side critical section!
> 
>  other info that might help us debug this:

This looks very complicated, why even bother ?

I gave an obvious patch fixing root cause, I have no idea why you prefer
over engineering this.

If you believe allocating peer netns id is required at link creation
time, you should explain why.

BTW, (void)peernet2id(dev_net(dev), src_net) can fail, and your fix is
not complete anyway.


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