linux-kernel - Re: [PATCH 1/4] Routine for generating an safe ID for kernel pointer

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Date:	Tue, 15 Nov 2011 13:51:34 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Pavel Emelyanov <xemul@...allels.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Glauber Costa <glommer@...allels.com>,
	Andi Kleen <andi@...stfloor.org>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Helsley <matthltc@...ibm.com>
Subject: Re: [PATCH 1/4] Routine for generating an safe ID for kernel pointer

On Tue, Nov 15, 2011 at 1:44 PM, Pavel Emelyanov <xemul@...allels.com> wrote:
>>> +unsigned long gen_object_id(void *ptr)
>>> +{
>>> +       if (!ptr)
>>> +               return 0;
>>> +
>>> +       if (unlikely(!ptr_poison)) {
>>> +               spin_lock(&ptr_poison_lock);
>>> +               if (!ptr_poison)
>>> +                       get_random_bytes(&ptr_poison, sizeof(ptr_poison));
>>> +               spin_unlock(&ptr_poison_lock);
>>> +       }
>>> +
>>> +       return ((unsigned long)ptr) ^ ptr_poison;
>>> +}
>>
>> You could put this in mm/util.c. Wouldn't it make sense to separate
>> the initialization and use late_initcall() to call it?
>
> OK, will put to util.c
>
> About the initialization - I will put the sanity check about poison being not 0 on
> get_object_id() anyway, so what's the point in separate initialization?

You no longer need the spinlock and you get rid of the potential
double initialization problem because you're not holding the spinlock
when you check for ptr_poisson being zero.

                        Pekka
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