linux-kernel - is dma_mapping_error() check necessary for dma_alloc

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Message-ID: <ff6c1fe6-820f-4e58-8395-df06aa91706c@oss.qualcomm.com>
Date: Tue, 26 Aug 2025 17:44:42 +0800
From: Baochen Qiang <baochen.qiang@....qualcomm.com>
To: Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Jeff Johnson <jjohnson@...nel.org>
Cc: iommu@...ts.linux.dev,
        "linux-kernel@...r.kernel.org >> linux-kernel"
 <linux-kernel@...r.kernel.org>,
        "ath11k@...ts.infradead.org" <ath11k@...ts.infradead.org>
Subject: is dma_mapping_error() check necessary for dma_alloc_noncoherent()?

Hi guys,

I have a driver which allocate noncoherent DMA buffer and get the returned CPU addr tested:

	vaddr_unaligned = dma_alloc_noncoherent(ab->dev, rx_tid->unaligned_size, &paddr,
						DMA_BIDIRECTIONAL, GFP_ATOMIC);
	if (!vaddr_unaligned) {
		spin_unlock_bh(&ab->base_lock);
		return -ENOMEM;
	}

while free the buffer

	dma_free_noncoherent(ab->dev, rx_tid->unaligned_size,
			     rx_tid->vaddr_unaligned,
			     rx_tid->paddr_unaligned, DMA_BIDIRECTIONAL);

I get below warnings:

 DMA-API: ath11k_pci 0000:03:00.0: device driver failed to check map error[device
address=0x00000000f3ad7000] [size=639 bytes] [mapped as single]
 WARNING: CPU: 15 PID: 64303 at kernel/dma/debug.c:1036 check_unmap+0x7e2/0x950
 RIP: 0010:check_unmap+0x7e2/0x950
 Call Trace:
  <TASK>
  ? free_to_partial_list+0x9d/0x350
  debug_dma_unmap_page+0xac/0xc0
  ? debug_smp_processor_id+0x17/0x20
  ? rcu_is_watching+0x13/0x70
  dma_free_pages+0x56/0x180
  [...]
  </TASK>
 ---[ end trace 0000000000000000 ]---
 DMA-API: Mapped at:
  debug_dma_map_page+0x7c/0x140
  dma_alloc_pages+0x74/0x220
  [...]

Checking code gives me the impression that I should do dma_mapping_error() check as well.
And indeed with below diff the warning is gone:

+       dma_mapping_error(ab->dev, paddr);

However this does not make sense to me since IMO testing the CPU address is good enough, I
can not imagine a valid case where DMA alloc/map fails while returning a valid CPU
address, no?

If I was right, should we remove invocation to debug_dma_map_page() in dma_alloc_pages()?