Re: [PATCH v3 1/2] dma-direct: provide the ability to reserve per-numa CMA

[Christoph Hellwig <hch@lst.de>]

On Wed, Jul 22, 2020 at 09:41:50PM +0000, Song Bao Hua (Barry Song) wrote:
> I got a kernel robot warning which said dev should be checked before being accessed
> when I did a similar change in v1. Probably it was an invalid warning if dev should
> never be null.

That usually shows up if a function is inconsistent about sometimes
checking it and sometimes now.

> Yes, it looks much better.

Below is a prep patch to rebase on top of:

---
From b81a5e1da65fce9750f0a8b66dbb6f842cbfdd4d Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Wed, 22 Jul 2020 16:33:43 +0200
Subject: dma-contiguous: cleanup dma_alloc_contiguous

Split out a cma_alloc_aligned helper to deal with the "interesting"
calling conventions for cma_alloc, which then allows to the main
function to be written straight forward.  This also takes advantage
of the fact that NULL dev arguments have been gone from the DMA API
for a while.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 kernel/dma/contiguous.c | 31 ++++++++++++++-----------------
 1 file changed, 14 insertions(+), 17 deletions(-)

diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 15bc5026c485f2..cff7e60968b9e1 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -215,6 +215,13 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
 	return cma_release(dev_get_cma_area(dev), pages, count);
 }
 
+static struct page *cma_alloc_aligned(struct cma *cma, size_t size, gfp_t gfp)
+{
+	unsigned int align = min(get_order(size), CONFIG_CMA_ALIGNMENT);
+
+	return cma_alloc(cma, size >> PAGE_SHIFT, align, gfp & __GFP_NOWARN);
+}
+
 /**
  * dma_alloc_contiguous() - allocate contiguous pages
  * @dev:   Pointer to device for which the allocation is performed.
@@ -231,24 +238,14 @@ bool dma_release_from_contiguous(struct device *dev, struct page *pages,
  */
 struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
 {
-	size_t count = size >> PAGE_SHIFT;
-	struct page *page = NULL;
-	struct cma *cma = NULL;
-
-	if (dev && dev->cma_area)
-		cma = dev->cma_area;
-	else if (count > 1)
-		cma = dma_contiguous_default_area;
-
 	/* CMA can be used only in the context which permits sleeping */
-	if (cma && gfpflags_allow_blocking(gfp)) {
-		size_t align = get_order(size);
-		size_t cma_align = min_t(size_t, align, CONFIG_CMA_ALIGNMENT);
-
-		page = cma_alloc(cma, count, cma_align, gfp & __GFP_NOWARN);
-	}
-
-	return page;
+	if (!gfpflags_allow_blocking(gfp))
+		return NULL;
+	if (dev->cma_area)
+		return cma_alloc_aligned(dev->cma_area, size, gfp);
+	if (size <= PAGE_SIZE || !dma_contiguous_default_area)
+		return NULL;
+	return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
 }
 
 /**
-- 
2.27.0

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