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Wed, 24 Mar 2021 18:35:00 +0000 Subject: Re: [RFC PATCH v2 04/11] PCI/P2PDMA: Introduce pci_p2pdma_should_map_bus() and pci_p2pdma_bus_offset() To: Jason Gunthorpe , 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 , Ira Weiny , John Hubbard , Don Dutile , Matthew Wilcox , Daniel Vetter , Jakowski Andrzej , Minturn Dave B , Jason Ekstrand , Dave Hansen , Xiong Jianxin 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> <20210324172157.GH2710221@ziepe.ca> From: =?UTF-8?Q?Christian_K=c3=b6nig?= Message-ID: <044e4f2b-6cb9-7740-622c-ec807bb1a79b@amd.com> Date: Wed, 24 Mar 2021 19:34:53 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 In-Reply-To: <20210324172157.GH2710221@ziepe.ca> Content-Type: text/plain; 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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. The only justification I can see for a "panic on warn" is to prevent further data loss or warn early about a crash. We only use a BUG_ON() when the alternative would be to corrupt something. Christian. > > Jason