net: mediatek: use dma_zalloc_coherent instead of allocator/memset

Commit Message

Yue Haibing July 20, 2018, 1:59 p.m. UTC

On 2018/7/20 21:48, Sean Wang wrote:
> On Fri, 2018-07-20 at 09:13 +0100, Russell King - ARM Linux wrote:
>> On Fri, Jul 20, 2018 at 02:30:53PM +0800, YueHaibing wrote:
>>> On 2018/7/20 1:02, Sean Wang wrote:
>>>> On Thu, 2018-07-19 at 15:17 +0100, Russell King - ARM Linux wrote:
>>>>> On Thu, Jul 19, 2018 at 10:09:55PM +0800, YueHaibing wrote:
>>>>>> Use dma_zalloc_coherent instead of dma_alloc_coherent
>>>>>> followed by memset 0.
>>>>>>
>>>>>> Signed-off-by: YueHaibing <[e-mail]>
>>>>>> ---
>>>>>>  drivers/net/ethernet/mediatek/mtk_eth_soc.c | 7 ++-----
>>>>>>  1 file changed, 2 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>>>>>> index d8ebf0a..fbdb3e3 100644
>>>>>> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>>>>>> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
>>>>>> @@ -1221,14 +1221,11 @@ static int mtk_tx_alloc(struct mtk_eth *eth)
>>>>>>  	if (!ring->buf)
>>>>>>  		goto no_tx_mem;
>>>>>>  
>>>>>> -	ring->dma = dma_alloc_coherent(eth->dev,
>>>>>> -					  MTK_DMA_SIZE * sz,
>>>>>> -					  &ring->phys,
>>>>>> -					  GFP_ATOMIC | __GFP_ZERO);
>>>>>> +	ring->dma = dma_zalloc_coherent(eth->dev, MTK_DMA_SIZE * sz,
>>>>>> +					&ring->phys, GFP_ATOMIC | __GFP_ZERO);
>>>>>>  	if (!ring->dma)
>>>>>>  		goto no_tx_mem;
>>>>>>  
>>>>>> -	memset(ring->dma, 0, MTK_DMA_SIZE * sz);
>>>>>
>>>>> I have to wonder whether this code needs two forms of zeroing... in
>>>>> the original code, __GFP_ZERO _and_ a call to memset() just in case
>>>>> __GFP_ZERO failed to do its job, and in the replacement code, just
>>>>> in case dma_zalloc_coherent() hasn't got the idea...
>>>>>
>>>>> I think you can drop the __GFP_ZERO. ;)
>>>>>
>>>>
>>>> Just now I did an experiment on 4.14.56 on armv7. I found that
>>>> dma_zalloc_coherent does not guarantee that the buffer we get
>>>> is all filled with 0.
>>>>
>>>>
>>>> I really think it's a little bit weird OR what was I missing something
>>>> for enabling dma_zalloc_coherent ? The result seems to tell that we
>>>> can't remove freely the memset with 0 at this moment until we get a
>>>> cause.
>>>>
>>>
>>> That means dma_zalloc_coherent doesn't work as expect on armv7?
>>
>> Can someone work out which underlying allocator is being used - the
>> possibilities are:
>>
>> - dma_alloc_from_dev_coherent
>> - cma
>> - simple
>> - remap
>> - pool
>>
>> Looking at the code, I'd guess it's the pool allocator, as I don't see
>> anything which zeros memory there, and it doesn't honor the __GFP_ZERO
>> flag.  This is definitely an allocator bug.
>>

Sean,

can you test bellow patch：

> Yes, your guess is right. the allocator is from pool. I show the full
> stack as below when calling dma_zalloc_coherent
> 
> [   54.358310] [<c0113ca8>] (unwind_backtrace) from [<c010e558>] (show_stack+0x20/0x24)
> [   54.366012] [<c010e558>] (show_stack) from [<c0927f58>] (dump_stack+0x98/0xac)
> [   54.373196] [<c0927f58>] (dump_stack) from [<c011c1f8>] (pool_allocator_alloc+0x20/0x30)
> [   54.381238] [<c011c1f8>] (pool_allocator_alloc) from [<c011a238>] (__dma_alloc+0x1b8/0x344)
> [   54.389538] [<c011a238>] (__dma_alloc) from [<c011a45c>] (arm_dma_alloc+0x50/0x58)
> [   54.397063] [<c011a45c>] (arm_dma_alloc) from [<c05dc208>] (mtk_open+0xf4/0x710)
> [   54.404416] [<c05dc208>] (mtk_open) from [<c076d110>] (__dev_open+0xdc/0x160)
> [   54.411507] [<c076d110>] (__dev_open) from [<c076d530>] (__dev_change_flags+0x178/0x1c4)
> [   54.419547] [<c076d530>] (__dev_change_flags) from [<c076d5a4>] (dev_change_flags+0x28/0x58)
> [   54.427934] [<c076d5a4>] (dev_change_flags) from [<c07ea7c0>] (devinet_ioctl+0x630/0x720)
> [   54.436062] [<c07ea7c0>] (devinet_ioctl) from [<c07ed070>] (inet_ioctl+0x210/0x3a8)
> [   54.443674] [<c07ed070>] (inet_ioctl) from [<c0747094>] (sock_ioctl+0x234/0x4dc)
> [   54.451029] [<c0747094>] (sock_ioctl) from [<c028206c>] (do_vfs_ioctl+0xc0/0x914)
> [   54.458468] [<c028206c>] (do_vfs_ioctl) from [<c0282904>] (SyS_ioctl+0x44/0x6c)
> [   54.465733] [<c0282904>] (SyS_ioctl) from [<c0101000>] (ret_fast_syscall+0x0/0x54)
> 
> 
> 
> 
> .
>

Patch

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index be0fa7e..52029bb 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -564,6 +564,7 @@  static void *__alloc_from_pool(size_t size, struct page **ret_page)

*ret_page = phys_to_page(phys);
ptr = (void *)val;
+ memset(ptr, 0, size);
}

>