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From: John Hsu <john.hsu@mediatek.com>
To: Christoph Hellwig <hch@lst.de>, Marek Szyprowski
	<m.szyprowski@samsung.com>, Robin Murphy <robin.murphy@arm.com>, "Matthias
 Brugger" <matthias.bgg@gmail.com>, AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>
CC: <surenb@google.com>, John Hsu <john.hsu@mediatek.com>, Chinwen Chang
	<chinwen.change@mediatek.com>, Casper Li <casper.li@mediatek.com>, "Kuan-Ying
 Lee" <Kuan-Ying.Lee@mediatek.com>, <iommu@lists.linux.dev>,
	<linux-kernel@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
	<linux-mediatek@lists.infradead.org>
Subject: [PATCH] direct-dma: WARN_ON_ONCE when the page is not addressable by device's coherent_dma_mask
Date: Wed, 13 Mar 2024 20:19:30 +0800
Message-ID: <20240313121933.15839-1-john.hsu@mediatek.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain

From: JohnHsu <john.hsu@mediatek.com>

The dma_direct_alloc() may return null in some cases. For example, the
allocated page is not addressable for the device's coherent_dma_mask,
and the allocated page will be assigned to null.

This patch can WARN_ON_ONCE() when the returned page is null in
dma_direct_alloc. It helps the developers position the root cause of
allocation failure rapidly.

Signed-off-by: JohnHsu <john.hsu@mediatek.com>
---
 kernel/dma/direct.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 9596ae1aa0da..a73b8ad1ef9e 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -156,6 +156,8 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
 		}
 	}
 
+	WARN_ON_ONCE(!page);
+
 	return page;
 }
 
-- 
2.18.0