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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3276f59e29csm4065656a91.12.2025.08.27.23.32.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 27 Aug 2025 23:32:16 -0700 (PDT) Message-ID: Date: Thu, 28 Aug 2025 14:32:11 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: is dma_mapping_error() check necessary for dma_alloc_noncoherent()? To: Christoph Hellwig Cc: Marek Szyprowski , Robin Murphy , Jeff Johnson , iommu@lists.linux.dev, "linux-kernel@vger.kernel.org >> linux-kernel" , "ath11k@lists.infradead.org" References: Content-Language: en-US From: Baochen Qiang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwODIzMDAzNCBTYWx0ZWRfX2ZMoaYa58Vi3 Ji2MDTsxRxmpbMzWlVnGlu/ZXMIS1MTp8UYiJyxdglwXWpu2M2RXvMlmZUkSGI+P/b90RXMY4l7 pkqY3Wf6SeZDEeabtS9lhNGsIHmibIic6VBLgT4pKoJnCR83HIXk06Srw4QPhv1BLLWofTtkbjY 3TmmqwVH2G+Ynm0S0MY7BQ5kiI35f7F4ubuZU7pBfJiJybZaCBAN3tFqvo+R0RMXN0eqy1f4BT9 WesGHzg9GvsauNJn9Rnv5Pd+GuzR9oNn4mg8PK4hi3eXh3nOmkeOQcVOxorfRdI5MmfZ51sAYpp OQJBKepO2d8Q4hwjrn1sBn+xUjszUNToXFONqU0SZd+Ud3v1H1qBYYBIaEohVos/ncn18BPXLUk refK0uM2 X-Proofpoint-GUID: FvOgC4M_4wP9cYJI4B13XnCUD-l4ZSyq X-Authority-Analysis: v=2.4 cv=K+AiHzWI c=1 sm=1 tr=0 ts=68aff7f2 cx=c_pps a=RP+M6JBNLl+fLTcSJhASfg==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=2OwXVqhp2XgA:10 a=d_vTzFHel96VW_NBT_kA:9 a=QEXdDO2ut3YA:10 a=iS9zxrgQBfv6-_F4QbHw:22 X-Proofpoint-ORIG-GUID: FvOgC4M_4wP9cYJI4B13XnCUD-l4ZSyq X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-08-28_01,2025-08-26_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 bulkscore=0 clxscore=1015 adultscore=0 impostorscore=0 priorityscore=1501 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2507300000 definitions=main-2508230034 On 8/27/2025 3:31 PM, Christoph Hellwig wrote: > On Tue, Aug 26, 2025 at 05:44:42PM +0800, Baochen Qiang wrote: >> 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? > > Yes, this doesn't make sense. dma_mapping_error exists to provide a > error handling path for dma_map_*, which return the dma address only. > > For the dma_alloc_* interfaces that return a pointer and can signal > with a NULL return it should not be needed and dma-debug needs to > be fixed. > >> If I was right, should we remove invocation to debug_dma_map_page() in dma_alloc_pages()? >> > > That allocation still needs to be tracked, so it can't just be removed > but needs to be changed to record the kind of allocation. Thanks, I will submit a patch to fix this.