linux-kernel - Re: [Patch] lkdtm: avoid calling lkdtm_do

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Message-ID: <4F28AB24.8050600@gmail.com>
Date:	Wed, 01 Feb 2012 11:01:56 +0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Prarit Bhargava <prarit@...hat.com>,
	Greg Kroah-Hartman <greg@...ah.com>
Subject: Re: [Patch] lkdtm: avoid calling lkdtm_do_action() with spin lock
 held

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?

>
> Can't you just get rid of the count_lock if you use an atomic_t for the
> count and use appropriate accesses on it?
>

Good idea, will do.

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