netdev - Re: [RFC PATCH net 1/2] [BUGFIX] bonding: use local function pointer of bond->recv_probe in bond_handle

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Date:	Tue, 11 Oct 2011 22:02:11 +0900
From:	HAYASAKA Mitsuo <mitsuo.hayasaka.hu@...achi.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Jay Vosburgh <fubar@...ibm.com>,
	Andy Gospodarek <andy@...yhouse.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, yrl.pp-manager.tt@...achi.com
Subject: Re: [RFC PATCH net 1/2] [BUGFIX] bonding: use local function pointer
 of bond->recv_probe in bond_handle_frame

Hi WANG Cong

Thank you for your comments.

(2011/10/07 22:24), Américo Wang wrote:
> On Fri, Oct 7, 2011 at 8:49 PM, Mitsuo Hayasaka
> <mitsuo.hayasaka.hu@...achi.com> wrote:
>> The bond->recv_probe is called in bond_handle_frame() when
>> a packet is received, but bond_close() sets it to NULL. So,
>> a panic occurs when both functions work in parallel.
>>
>> Why this happen:
>> After null pointer check of bond->recv_probe, an sk_buff is
>> duplicated and bond->recv_probe is called in bond_handle_frame.
>> So, a panic occurs when bond_close() is called between the
>> check and call of bond->recv_probe.
>>
>> Patch:
>> This patch uses a local function pointer of bond->recv_probe
>> in bond_handle_frame(). So, it can avoid the null pointer
>> dereference.
>>
> 
> Hmm, I don't doubt it can fix the problem, I am wondering if
> bond->recv_probe should be protected by bond->lock...

Indeed, in general any resources should be protected from the asynchronous
workers.

At first, I thought it should be handled with lock protection, as well.
However, I guess that using bond->lock on this kind of hot-path may
introduces unnecessary overhead. In addition, this code works well
without the strict lock protection. So, I think this change is the
right way to fix it.

Thanks.
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