Re: [PATCH v1] ALSA: memalloc: Fix indefinite hang in non-iommu case

[Hillf Danton <hdanton@xxxxxxxx>]

On Thu, 15 Feb 2024 18:03:01 +0100 Takashi Iwai <tiwai@xxxxxxx> wrote:
> 
> So it sounds like that we should go back for __GFP_NORETRY in general
> for non-zero order allocations, not only the call you changed, as
> __GFP_RETRY_MAYFAIL doesn't guarantee the stuck.
> 
> How about the changes like below?
> 
> +/* default GFP bits for our allocations */
> +static gfp_t default_gfp(size_t size)
> +{
> +	/* don't allocate intensively for high-order pages */
> +	if (size > PAGE_SIZE)
> +		return GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY;
> +	else
> +		return GFP_KERNEL | __GFP_NOWARN | __GFP_RETRY_MAYFAIL;
> +}

Looks like an overdose because both __GFP_NORETRY and __GFP_RETRY_MAYFAIL
are checked in __alloc_pages_slowpath().

--- x/sound/core/memalloc.c
+++ y/sound/core/memalloc.c
@@ -540,13 +540,20 @@ static void *snd_dma_noncontig_alloc(str
 {
 	struct sg_table *sgt;
 	void *p;
+	gfp_t gfp = DEFAULT_GFP;
 
 #ifdef CONFIG_SND_DMA_SGBUF
 	if (cpu_feature_enabled(X86_FEATURE_XENPV))
 		return snd_dma_sg_fallback_alloc(dmab, size);
+	/*
+	 * Given fallback, quit allocation in case of PAGE_ALLOC_COSTLY_ORDER with
+	 * lower orders handled by page allocator
+	 */
+	if (!get_dma_ops(dmab->dev.dev))
+		gfp &= ~__GFP_RETRY_MAYFAIL;
 #endif
-	sgt = dma_alloc_noncontiguous(dmab->dev.dev, size, dmab->dev.dir,
-				      DEFAULT_GFP, 0);
+	sgt = dma_alloc_noncontiguous(dmab->dev.dev, size, dmab->dev.dir, gfp, 0);
+
 #ifdef CONFIG_SND_DMA_SGBUF
 	if (!sgt && !get_dma_ops(dmab->dev.dev))
 		return snd_dma_sg_fallback_alloc(dmab, size);