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

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Message-ID: <877glhkm6b.fsf@xmission.com>
Date:	Sat, 09 Mar 2013 00:33:00 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Rakib Mullick <rakib.mullick@...il.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

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.

Eric
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