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Date: Thu, 02 Feb 2012 21:31:03 +0800
From: Cong Wang <xiyou.wangcong@gmail.com>
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To: Arnd Bergmann <arnd@arndb.de>
CC: Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org,
        Prarit Bhargava <prarit@redhat.com>,
        Greg Kroah-Hartman <greg@kroah.com>
Subject: Re: [Patch] lkdtm: avoid calling lkdtm_do_action() with spin lock
 held
References: <1327755168-12240-1-git-send-email-xiyou.wangcong@gmail.com> <201201311535.53526.arnd@arndb.de> <4F28AB24.8050600@gmail.com> <201202011529.32778.arnd@arndb.de>
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On 02/01/2012 11:29 PM, Arnd Bergmann wrote:
> On Wednesday 01 February 2012, Cong Wang wrote:
>> On 01/31/2012 11:35 PM, Arnd Bergmann wrote:
>>> On Tuesday 31 January 2012, Cong Wang wrote:
>>>> @@ -323,14 +323,16 @@ static void lkdtm_do_action(enum ctype which)
>>>>           }
>>>>           case CT_WRITE_AFTER_FREE: {
>>>>                   size_t len = 1024;
>>>> -               u32 *data = kmalloc(len, GFP_KERNEL);
>>>> +               u32 *data = kmalloc(len, GFP_ATOMIC);
>>>>
>>>>                   kfree(data);
>>>> -               schedule();
>>>> +               udelay(100);
>>>>                   memset(data, 0x78, len);
>>>>                   break;
>>>>           }
>>>
>>> I can't think of why the udelay would have any positive effect here,
>>> if the idea of the schedule was to let some other process allocate and
>>> use the memory.
>>
>>
>> Hmm, on SMP udelay on this CPU will give a chance to other CPU's to use
>> that memory, right?
>>
>
> There is a small chance for that, but it's much less likely than it would
> be using another process on the same CPU, plus it requires SMP.

Yeah, I updated this in [PATCH 2/2] lkdtm: avoid calling sleeping 
functions in interrupt context.