On Wed, 20 Apr 2022 09:44:58 +0200,
Dan Carpenter wrote:
>
> Hello Takashi Iwai,
>
> The patch 925ca893b4a6: "ALSA: memalloc: Add fallback SG-buffer
> allocations for x86" from Apr 13, 2022, leads to the following Smatch
> static checker warning:
>
> sound/core/memalloc.c:732 snd_dma_sg_fallback_alloc()
> error: 'p' came from dma_alloc_coherent() so we can't do virt_to_phys()
>
> sound/core/memalloc.c
> 708 static void *snd_dma_sg_fallback_alloc(struct snd_dma_buffer *dmab, size_t size)
> 709 {
> 710 struct snd_dma_sg_fallback *sgbuf;
> 711 struct page **pages;
> 712 size_t i, count;
> 713 void *p;
> 714
> 715 sgbuf = kzalloc(sizeof(*sgbuf), GFP_KERNEL);
> 716 if (!sgbuf)
> 717 return NULL;
> 718 count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> 719 pages = kvcalloc(count, sizeof(*pages), GFP_KERNEL);
> 720 if (!pages)
> 721 goto error;
> 722 sgbuf->pages = pages;
> 723 sgbuf->addrs = kvcalloc(count, sizeof(*sgbuf->addrs), GFP_KERNEL);
> 724 if (!sgbuf->addrs)
> 725 goto error;
> 726
> 727 for (i = 0; i < count; sgbuf->count++, i++) {
> 728 p = dma_alloc_coherent(dmab->dev.dev, PAGE_SIZE,
> 729 &sgbuf->addrs[i], DEFAULT_GFP);
> 730 if (!p)
> 731 goto error;
> --> 732 sgbuf->pages[i] = virt_to_page(p);
>
> The warning is a bit useless. It's complaining about __phys_addr()
> and not virt_to_phys(). I don't really understand the rules here, it
> might be legal in certain contexts.
In general it's not good to perform virt_to_page() for the
dma_alloc_coherent(), but here the code is special only for x86 and
certain circumstances, so this must work -- it's the very same stuff
we had over a decade, after all. The code was resurrected in a
simplified form as a fallback now.
thanks,
Takashi
