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08 Nov 2018 16:48:58 -0600 Received: from pps.filterd (m0144104.ppops.net [127.0.0.1]) by mx0b-00154901.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wA8Mm9WN167538 for ; Thu, 8 Nov 2018 17:49:12 -0500 Received: from esa2.dell-outbound2.iphmx.com (esa2.dell-outbound2.iphmx.com [68.232.153.202]) by mx0b-00154901.pphosted.com with ESMTP id 2nmtq09323-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Thu, 08 Nov 2018 17:49:12 -0500 Received: from ausc60pc101.us.dell.com ([143.166.85.206]) by esa2.dell-outbound2.iphmx.com with ESMTP/TLS/DHE-RSA-AES256-SHA256; 09 Nov 2018 04:48:59 +0600 X-LoopCount0: from 10.166.134.87 X-IronPort-AV: E=Sophos;i="5.54,481,1534827600"; d="scan'208";a="1323441867" From: To: , Subject: Re: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected Thread-Topic: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected Thread-Index: AQHUT50UQ290XPGvJEGnaSTTjbCF+g== Date: Thu, 8 Nov 2018 22:49:08 +0000 Message-ID: <20d68e586fff4dcca5616d5056f6fc21@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> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.177.90.70] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2018-11-08_13:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1811080192 X-Mailman-Approved-At: Fri, 09 Nov 2018 13:29:42 +1100 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: sbobroff@linux.ibm.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Shyam.Iyer@dell.com, lukas@wunner.de, helgaas@kernel.org, mr.nuke.me@gmail.com, Austin.Bolen@dell.com, oohall@gmail.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 11/08/2018 04:43 PM, Greg Kroah-Hartman wrote:=0A= > =0A= > [EXTERNAL EMAIL]=0A= > Please report any suspicious attachments, links, or requests for sensitiv= e information.=0A= > =0A= > =0A= > On Thu, Nov 08, 2018 at 03:32:58PM -0700, Keith Busch wrote:=0A= >> On Thu, Nov 08, 2018 at 02:01:17PM -0800, Greg Kroah-Hartman wrote:=0A= >>> On Thu, Nov 08, 2018 at 02:09:17PM -0600, Bjorn Helgaas wrote:=0A= >>>> I'm having second thoughts about this. One thing I'm uncomfortable=0A= >>>> with is that sprinkling pci_dev_is_disconnected() around feels ad hoc= =0A= >>>> instead of systematic, in the sense that I don't know how we convince= =0A= >>>> ourselves that this (and only this) is the correct place to put it.=0A= >>>=0A= >>> I think my stance always has been that this call is not good at all=0A= >>> because once you call it you never really know if it is still true as= =0A= >>> the device could have been removed right afterward.=0A= >>>=0A= >>> So almost any code that relies on it is broken, there is no locking and= =0A= >>> it can and will race and you will loose.=0A= >>=0A= >> AIUI, we're not trying to create code to rely on this. This more about= =0A= >> reducing reliance on hardware. If the software misses the race once and= =0A= >> accesses disconnected device memory, that's usually not a big deal to=0A= >> let hardware sort it out, but the point is not to push our luck.=0A= > =0A= > Then why even care about this call at all? If you need to really know=0A= > if the read worked, you have to check the value. If the value is FF=0A= > then you have a huge hint that the hardware is now gone. And you can=0A= > rely on it being gone, you can never rely on making the call to the=0A= > function to check if the hardware is there to be still valid any point=0A= > in time after the call returns.=0A= =0A= In the case that we're trying to fix, this code executing is a result of = =0A= the device being gone, so we can guarantee race-free operation. I agree =0A= that there is a race, in the general case. As far as checking the result = =0A= for all F's, that's not an option when firmware crashes the system as a =0A= result of the mmio read/write. It's never pretty when firmware gets =0A= involved.=0A= =0A= Alex=0A=