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Wed, 24 Mar 2021 10:21:59 -0700 (PDT) Received: from ziepe.ca ([206.223.160.26]) by smtp.gmail.com with ESMTPSA id q125sm2144133qkf.68.2021.03.24.10.21.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Mar 2021 10:21:59 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1lP7Cf-0025Yq-Vy; Wed, 24 Mar 2021 14:21:58 -0300 Date: Wed, 24 Mar 2021 14:21:57 -0300 From: Jason Gunthorpe To: Logan Gunthorpe Cc: Ira Weiny , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, iommu@lists.linux-foundation.org, Stephen Bates , Christoph Hellwig , Dan Williams , Christian =?utf-8?B?S8O2bmln?= , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin Subject: Re: [RFC PATCH v2 04/11] PCI/P2PDMA: Introduce pci_p2pdma_should_map_bus() and pci_p2pdma_bus_offset() Message-ID: <20210324172157.GH2710221@ziepe.ca> References: <20210311233142.7900-1-logang@deltatee.com> <20210311233142.7900-5-logang@deltatee.com> <20210313013856.GA3402637@iweiny-DESK2.sc.intel.com> <7509243d-b605-953b-6941-72876a60d527@deltatee.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7509243d-b605-953b-6941-72876a60d527@deltatee.com> X-Stat-Signature: 1ag7zcr7sq78apmhzpd4mfogb7fth6js X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 6B6FD40001FE Received-SPF: none (ziepe.ca>: No applicable sender policy available) receiver=imf02; identity=mailfrom; envelope-from=""; helo=mail-qt1-f173.google.com; client-ip=209.85.160.173 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616606523-690852 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Mar 15, 2021 at 10:27:08AM -0600, Logan Gunthorpe wrote: > In this case the WARN_ON is just to guard against misuse of the > function. It should never happen unless a developer changes the code in > a way that is incorrect. So I think that's the correct use of WARN_ON. > Though I might change it to WARN and return, that seems safer. Right, WARN_ON and return is the right pattern for an assertion that must never happen: if (WARN_ON(foo)) return -1 Linus wants assertions like this to be able to recover. People runing the 'panic on warn' mode want the kernel to stop if it detects an internal malfunction. Jason