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Sun, 11 Nov 2018 21:50:06 -0800 (PST) Message-ID: <5da8d8aa9f3818af649b1ac547bc4e6062626ddf.camel@gmail.com> Subject: Re: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected From: Oliver O'Halloran To: Alex_Gagniuc@Dellteam.com, gregkh@linuxfoundation.org Date: Mon, 12 Nov 2018 16:49:59 +1100 In-Reply-To: <16bf9d14bc5f4a90b2b88dd2eb165186@ausx13mps321.AMER.DELL.COM> References: <20180918221501.13112-1-mr.nuke.me@gmail.com> <20181107234257.GC41183@google.com> <20181108200855.GE41183@google.com> <20181108220117.GA11466@kroah.com> <20181108223258.GD2932@localhost.localdomain> <20181108224255.GA20619@kroah.com> <20d68e586fff4dcca5616d5056f6fc21@ausx13mps321.AMER.DELL.COM> <20181108225109.GA3023@kroah.com> <16bf9d14bc5f4a90b2b88dd2eb165186@ausx13mps321.AMER.DELL.COM> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Shyam.Iyer@dell.com, sbobroff@linux.ibm.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, keith.busch@intel.com, lukas@wunner.de, helgaas@kernel.org, mr.nuke.me@gmail.com, Austin.Bolen@dell.com, linuxppc-dev@lists.ozlabs.org, jonathan.derrick@intel.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, 2018-11-08 at 23:06 +0000, Alex_Gagniuc@Dellteam.com wrote: > On 11/08/2018 04:51 PM, Greg KH wrote: > > On Thu, Nov 08, 2018 at 10:49:08PM +0000, Alex_Gagniuc@Dellteam.com wrote: > > > In the case that we're trying to fix, this code executing is a result of > > > the device being gone, so we can guarantee race-free operation. I agree > > > that there is a race, in the general case. As far as checking the result > > > for all F's, that's not an option when firmware crashes the system as a > > > result of the mmio read/write. It's never pretty when firmware gets > > > involved. > > > > If you have firmware that crashes the system when you try to read from a > > PCI device that was hot-removed, that is broken firmware and needs to be > > fixed. The kernel can not work around that as again, you will never win > > that race. > > But it's not the firmware that crashes. It's linux as a result of a > fatal error message from the firmware. And we can't fix that because FFS > handling requires that the system reboots [1]. Do we know the exact circumsances that result in firmware requesting a reboot? If it happen on any PCIe error I don't see what we can do to prevent that beyond masking UEs entirely (are we even allowed to do that on FFS systems?). > If we're going to say that we don't want to support FFS because it's a > separate code path, and different flow, that's fine. I am myself, not a > fan of FFS. But if we're going to continue supporting it, I think we'll > continue to have to resolve these sort of unintended consequences. > > Alex > > [1] ACPI 6.2, 18.1 - Hardware Errors and Error Sources