linux-kernel - Re: [nsproxy] BUG: unable to handle kernel NULL pointer dereference at 0000000000000024

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Date:	Sat, 9 Mar 2013 22:48:43 +0600
From:	Rakib Mullick <rakib.mullick@...il.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [nsproxy] BUG: unable to handle kernel NULL pointer dereference
 at 0000000000000024

On Sat, Mar 9, 2013 at 2:33 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
> Rakib Mullick <rakib.mullick@...il.com> writes:
>
>> On Fri, Mar 8, 2013 at 10:01 PM, Eric W. Biederman
>> <ebiederm@...ssion.com> wrote:
>>>
>>> When a new task is created one of two things needs to happen.
>>> A) A reference count needs to be added to the current nsproxy.
>>> B) B a new nsproxy needs to be created.
>>>
>>> The way that code works today is far from a shiny example of totally
>>> clear code but it is not incorrect.
>>>
>>> By moving get_nsproxy down below the first return 0, you removed taking
>>> the reference count in the one case it is important.
>>>
>>> Arguably we should apply the patch below for clarity, and I just might
>>> queue it up for 3.10.
>>>
>> This one is much more cleaner. One thing regarding this patch, can we
>> check the namespace related flags at copy_namespace() call time at
>> copy_process(), also get_nsproxy()? I think this will reduce some
>> extra function call overhead and as you've mentioned get_nsproxy() is
>> needed at every process creation.
>
> If you can write a benchmark that can tell the difference, and the code
> continues to be readable.  It would be worth making the change.
>
> My gut says you are proposing an optimization that won't have
> a measurable impact.
>
Yes, it'll be hard to measure these sorts of optimization, though I'll
try and will tell you if the impact is measurable :).

Thanks,
Rakib.
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