linux-kernel - Re: [PATCH v2] dma_heap: use for_each_sgtable_sg in sg

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Date:   Thu, 25 Nov 2021 14:08:00 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     guangming.cao@...iatek.com
Cc:     Brian.Starkey@....com, benjamin.gaignard@...aro.org,
        christian.koenig@....com, dri-devel@...ts.freedesktop.org,
        john.stultz@...aro.org, labbott@...hat.com,
        linaro-mm-sig@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        lmark@...eaurora.org, matthias.bgg@...il.com,
        sumit.semwal@...aro.org, wsd_upstream@...iatek.com
Subject: Re: [PATCH v2] dma_heap: use for_each_sgtable_sg in sg_table release
 flow

On 2021-11-25 13:49, guangming.cao@...iatek.com wrote:
> From: Guangming <Guangming.Cao@...iatek.com>
> 
> Use (for_each_sgtable_sg) rather than (for_each_sg) to traverse
> sg_table to free sg_table.
> Use (for_each_sg) maybe will casuse some pages can't be freed
> when send wrong nents number.

It's still worth spelling out that this is fixing a bug where the 
current code should have been using table->orig_nents - it's just that 
switching to the sgtable helper is the best way to make the fix, since 
it almost entirely removes the possibility of making that (previously 
rather common) mistake.

If it helps, for the change itself:

Reviewed-by: Robin Murphy <robin.murphy@....com>

Thanks,
Robin.

> Signed-off-by: Guangming <Guangming.Cao@...iatek.com>
> ---
>   drivers/dma-buf/heaps/system_heap.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 23a7e74ef966..8660508f3684 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -289,7 +289,7 @@ static void system_heap_dma_buf_release(struct dma_buf *dmabuf)
>   	int i;
>   
>   	table = &buffer->sg_table;
> -	for_each_sg(table->sgl, sg, table->nents, i) {
> +	for_each_sgtable_sg(table, sg, i) {
>   		struct page *page = sg_page(sg);
>   
>   		__free_pages(page, compound_order(page));
>