linux-kernel - Re: [PATCH] scatterlist: prevent invalid free when alloc fails

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Message-ID: <AANLkTi=xAbbbyOLWG=3fJzeJo8FsvnQR5+M-LbG8cqtX@mail.gmail.com>
Date:	Fri, 27 Aug 2010 15:15:15 -0500
From:	Jeffrey Carlyle <jeff.carlyle@...orola.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	torvalds@...l.org, linux-kernel@...r.kernel.org,
	jaxboe@...ionio.com,
	OLUSANYA SOYANNWO <olusanya.soyannwo@...orola.com>,
	Hu Tao <taohu@...orola.com>
Subject: Re: [PATCH] scatterlist: prevent invalid free when alloc fails

On Fri, Aug 27, 2010 at 2:45 PM, Jeffrey Carlyle
<jeff.carlyle@...orola.com> wrote:
> On Fri, Aug 27, 2010 at 5:18 AM, Tejun Heo <tj@...nel.org> wrote:
>> On 08/26/2010 06:04 PM, Jeffrey Carlyle wrote:
>>> diff --git a/lib/scatterlist.c b/lib/scatterlist.c
>>> index a5ec428..acf2c6e 100644
>>> --- a/lib/scatterlist.c
>>> +++ b/lib/scatterlist.c
>>> @@ -163,7 +163,7 @@ void __sg_free_table(struct sg_table *table,
>>> unsigned int max_ents,
>>>               return;
>>>
>>>       sgl = table->sgl;
>>> -     while (table->orig_nents) {
>>> +     while (table->orig_nents && sgl) {
>>>               unsigned int alloc_size = table->orig_nents;
>>>               unsigned int sg_size;
>>
>> Why is this change necessary?
>
> Well the problem we were seeing manifested itself when we called
> free_fn on a NULL value. This was a naive attempt at avoiding that. If
> the logic in __sg_alloc_table is corrected, I agree that we shouldn't
> need this.

Actually, please disregard the comment about trying to free NULL. I
don't think we need to add the "&& sgl" under any circumstances.
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