linux-kernel - Re: [PATCH kernel v10 05/34] powerpc/iommu: Always release iommu_table in iommu_free

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Message-ID: <555409B8.3060904@ozlabs.ru>
Date:	Thu, 14 May 2015 12:34:32 +1000
From:	Alexey Kardashevskiy <aik@...abs.ru>
To:	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	Thomas Huth <thuth@...hat.com>
CC:	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH kernel v10 05/34] powerpc/iommu: Always release iommu_table
 in iommu_free_table()

On 05/14/2015 09:27 AM, Gavin Shan wrote:
> On Wed, May 13, 2015 at 02:51:36PM +0200, Thomas Huth wrote:
>> On Wed, 13 May 2015 16:30:16 +1000
>> Alexey Kardashevskiy <aik@...abs.ru> wrote:
>>
>>> On 05/13/2015 03:33 PM, Gavin Shan wrote:
>>>> On Tue, May 12, 2015 at 01:38:54AM +1000, Alexey Kardashevskiy wrote:
>>>>> At the moment iommu_free_table() only releases memory if
>>>>> the table was initialized for the platform code use, i.e. it had
>>>>> it_map initialized (which purpose is to track DMA memory space use).
>>>>>
>>>>> With dynamic DMA windows, we will need to be able to release
>>>>> iommu_table even if it was used for VFIO in which case it_map is NULL
>>>>> so does the patch.
>>>>>
>>>>> Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
>>>>
>>>> Reviewed-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>
>>>>
>>>>> ---
>>>>> arch/powerpc/kernel/iommu.c | 3 +--
>>>>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>>>>> index 3d47eb3..2c02d4c 100644
>>>>> --- a/arch/powerpc/kernel/iommu.c
>>>>> +++ b/arch/powerpc/kernel/iommu.c
>>>>> @@ -714,8 +714,7 @@ void iommu_free_table(struct iommu_table *tbl, const char *node_name)
>>>>> 	unsigned int order;
>>>>>
>>>>> 	if (!tbl || !tbl->it_map) {
>>>>> -		printk(KERN_ERR "%s: expected TCE map for %s\n", __func__,
>>>>> -				node_name);
>>>>> +		kfree(tbl);
>>>>
>>>> I'm not sure if the "tbl" needs to be checked against NULL as kfree() already
>>>> has the check. But it looks a bit strange to free NULL "tbl" from the code
>>>> itself.
>>>
>>> Yeah, looks a bit weird, agree, I'll change but in general kfree/vfree/...
>>> - they all check the passed pointer for NULL.
>>
>> But if tbl is NULL, the tbl->it_map check will fail, won't it? So in
>> this case, I think you have to keep it.
>>
>
> If I understood your question correctly, "tbl->it_map" won't be checked
> when "tbl" is NULL because the connection ("||") for the two conditions.
> The code can be changed to something like below if Alexey want:
>
> 	if (!tbl)
> 		return;
> 	if (!tbl->itmap)
> 		kfree(tbl);

To be precise ;)

if (!tbl->itmap) {
	kfree(tbl);
	return;
}

>
> Thanks,
> Gavin
>


-- 
Alexey
--
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