On Sat, Jun 27, 2020 at 01:45:16PM +0200, Richard Weinberger wrote:
> Hi!
>
> While porting on an old out-of-tree driver I noticed that dma_alloc_coherent()
> was used with dev being NULL.
>
> commit 148a97d5a02a62f81b5d6176f871c94a65e1f3af
> Author: Dan Carpenter <dan.carpen...@oracle.com>
> Date: Wed Apr 24 17:24:37 2019 +0300
>
> dma-mapping: remove an unnecessary NULL check
>
> We already dereferenced "dev" when we called get_dma_ops() so this NULL
> check is too late. We're not supposed to pass NULL "dev" pointers to
> dma_alloc_attrs().
>
> Signed-off-by: Dan Carpenter <dan.carpen...@oracle.com>
> Signed-off-by: Christoph Hellwig <h...@lst.de>
>
> says that dma_alloc_attrs() with dev being NULL is not allowed, but in
> include/linux/dma-mapping.h we have:
>
> static inline void *dma_alloc_coherent(struct device *dev, size_t size,
> dma_addr_t *dma_handle, gfp_t gfp)
> {
>
> return dma_alloc_attrs(dev, size, dma_handle, gfp,
> (gfp & __GFP_NOWARN) ? DMA_ATTR_NO_WARN : 0);
> }
>
> In Linus' tree I see at least three callers of dma_alloc_coherent() with a
> NULL device.
> drivers/staging/emxx_udc/emxx_udc.c:2596: ep->virt_buf
> = dma_alloc_coherent(NULL, PAGE_SIZE,
> drivers/tty/synclink.c:3667: info->buffer_list =
> dma_alloc_coherent(NULL, BUFFERLISTSIZE, &info->buffer_list_dma_addr,
> GFP_KERNEL);
> drivers/tty/synclink.c:3777: BufferList[i].virt_addr =
> dma_alloc_coherent(NULL, DMABUFFERSIZE, &BufferList[i].dma_addr, GFP_KERNEL);
>
> I think these callers are wrong.
> Can you please clarify?
The are wrong. It was slightly worse when I originally sent the patch
but we fixed comedi.
https://lkml.org/lkml/2019/4/24/668
regards,
dan carpenter
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