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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 2 Oct 2018 14:13:25 -0400 Received: from b01ledav006.gho.pok.ibm.com (b01ledav006.gho.pok.ibm.com [9.57.199.111]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w92IDPKE30212326 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Tue, 2 Oct 2018 18:13:25 GMT Received: from b01ledav006.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 879E7AC05F; Tue, 2 Oct 2018 14:12:42 -0400 (EDT) Received: from b01ledav006.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A537AAC065; Tue, 2 Oct 2018 14:12:40 -0400 (EDT) Received: from oc5000245537.ibm.com (unknown [9.53.179.212]) by b01ledav006.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 2 Oct 2018 14:12:40 -0400 (EDT) Subject: Re: [PATCH] migration/mm: Add WARN_ON to try_offline_node To: Michal Hocko Cc: Thomas Falcon , Kees Cook , Mathieu Malaterre , Pavel Tatashin , Nicholas Piggin , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Mauricio Faria de Oliveira , Juliet Kim , Tyrel Datwyler , Thiago Jung Bauermann , Nathan Fontenot , Andrew Morton , YASUAKI ISHIMATSU , linuxppc-dev@lists.ozlabs.org, Dan Williams , Oscar Salvador References: <20181001185616.11427.35521.stgit@ltcalpine2-lp9.aus.stglabs.ibm.com> <20181001202724.GL18290@dhcp22.suse.cz> <20181002145922.GZ18290@dhcp22.suse.cz> <20181002160446.GA18290@dhcp22.suse.cz> From: Michael Bringmann Openpgp: preference=signencrypt Autocrypt: addr=mwb@linux.vnet.ibm.com; prefer-encrypt=mutual; keydata= xsBNBFcY7GcBCADzw3en+yzo9ASFGCfldVkIg95SAMPK0myXp2XJYET3zT45uBsX/uj9/2nA lBmXXeOSXnPfJ9V3vtiwcfATnWIsVt3tL6n1kqikzH9nXNxZT7MU/7gqzWZngMAWh/GJ9qyg DTOZdjsvdUNUWxtiLvBo7y+reA4HjlQhwhYxxvCpXBeRoF0qDWfQ8DkneemqINzDZPwSQ7zY t4F5iyN1I9GC5RNK8Y6jiKmm6bDkrrbtXPOtzXKs0J0FqWEIab/u3BDrRP3STDVPdXqViHua AjEzthQbGZm0VCxI4a7XjMi99g614/qDcXZCs00GLZ/VYIE8hB9C5Q+l66S60PLjRrxnABEB AAHNLU1pY2hhZWwgVy4gQnJpbmdtYW5uIDxtd2JAbGludXgudm5ldC5pYm0uY29tPsLAeAQT AQIAIgUCVxjsZwIbAwYLCQgHAwIGFQgCCQoLBBYCAwECHgECF4AACgkQSEdag3dpuTI0NAf8 CKYTDKQLgOSjVrU2L5rM4lXaJRmQV6oidD3vIhKSnWRvPq9C29ifRG6ri20prTHAlc0vycgm 41HHg0y2vsGgNXGTWC2ObemoZBI7mySXe/7Tq5mD/semGzOp0YWZ7teqrkiSR8Bw0p+LdE7K QmT7tpjjvuhrtQ3RRojUYcuy1nWUsc4D+2cxsnZslsx84FUKxPbLagDgZmgBhUw/sUi40s6S AkdViVCVS0WANddLIpG0cfdsV0kCae/XdjK3mRK6drFKv1z+QFjvOhc8QIkkxFD0da9w3tJj oqnqHFV5gLcHO6/wizPx/NV90y6RngeBORkQiRFWxTXS4Oj9GVI/Us7ATQRXGOxnAQgAmJ5Y ikTWrMWPfiveUacETyEhWVl7u8UhZcx3yy2te8O0ay7t9fYcZgIEfQPPVVus89acIXlG3wYL DDPvb21OprLxi+ZJ2a0S5we+LcSWN1jByxJlbWBq+/LcMtGAOhNLpysY1gD0Y4UW/eKS+TFZ 562qKC3k1dBvnV9JXCgeS1taYFxRdVAn+2DwK3nuyG/DDq/XgJ5BtmyC3MMx8CiW3POj+O+l 6SedIeAfZlZ7/xhijx82g93h07VavUQRwMZgZFsqmuxBxVGiav2HB+dNvs3PFB087Pvc9OHe qhajPWOP/gNLMmvBvknn1NToM9a8/E8rzcIZXoYs4RggRRYh6wARAQABwsBfBBgBAgAJBQJX GOxnAhsMAAoJEEhHWoN3abky+RUH/jE08/r5QzaNKYeVhu0uVbgXu5fsxqr2cAxhf+KuwT3T efhEP2alarxzUZdEh4MsG6c+X2NYLbD3cryiXxVx/7kSAJEFQJfA5P06g8NLR25Qpq9BLsN7 ++dxQ+CLKzSEb1X24hYAJZpOhS8ev3ii+M/XIo+olDBKuTaTgB6elrg3CaxUsVgLBJ+jbRkW yQe2S5f/Ja1ThDpSSLLWLiLK/z7+gaqwhnwjQ8Z8Y9D2itJQcj4itHilwImsqwLG7SxzC0NX IQ5KaAFYdRcOgwR8VhhkOIVd70ObSZU+E4pTET1WDz4o65xZ89yfose1No0+r5ht/xWOOrh8 53/hcWvxHVs= Organization: IBM Linux Technology Center Date: Tue, 2 Oct 2018 13:13:22 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181002160446.GA18290@dhcp22.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18100218-0064-0000-0000-00000358DBDF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009810; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000267; SDB=6.01096894; UDB=6.00567221; IPR=6.00876936; MB=3.00023591; MTD=3.00000008; XFM=3.00000015; UTC=2018-10-02 18:13:29 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18100218-0065-0000-0000-00003AD8B2A9 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-10-02_08:,, 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-1810020173 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02/2018 11:04 AM, Michal Hocko wrote: > On Tue 02-10-18 10:14:49, Michael Bringmann wrote: >> On 10/02/2018 09:59 AM, Michal Hocko wrote: >>> On Tue 02-10-18 09:51:40, Michael Bringmann wrote: >>> [...] >>>> When the device-tree affinity attributes have changed for memory, >>>> the 'nid' affinity calculated points to a different node for the >>>> memory block than the one used to install it, previously on the >>>> source system. The newly calculated 'nid' affinity may not yet >>>> be initialized on the target system. The current memory tracking >>>> mechanisms do not record the node to which a memory block was >>>> associated when it was added. Nathan is looking at adding this >>>> feature to the new implementation of LMBs, but it is not there >>>> yet, and won't be present in earlier kernels without backporting a >>>> significant number of changes. >>> >>> Then the patch you have proposed here just papers over a real issue, no? >>> IIUC then you simply do not remove the memory if you lose the race. >> >> The problem occurs when removing memory after an affinity change >> references a node that was previously unreferenced. Other code >> in 'kernel/mm/memory_hotplug.c' deals with initializing an empty >> node when adding memory to a system. The 'removing memory' case is >> specific to systems that perform LPM and allow device-tree changes. >> The powerpc kernel does not have the option of accepting some PRRN >> requests and accepting others. It must perform them all. > > I am sorry, but you are still too cryptic for me. Either there is a > correctness issue and the the patch doesn't really fix anything or the > final race doesn't make any difference and then the ppc code should be > explicit about that. Checking the node inside the hotplug core code just > looks as a wrong layer to mitigate an arch specific problem. I am not > saying the patch is a no-go but if anything we want a big fat comment > explaining how this is possible because right now it just points to an > incorrect API usage. > > That being said, this sounds pretty much ppc specific problem and I > would _prefer_ it to be handled there (along with a big fat comment of > course). Let me try again. Regardless of the path to which we get to this condition, we currently crash the kernel. This patch changes that to a WARN_ON notice and continues executing the kernel without shutting down the system. I saw the problem during powerpc testing, because that is the focus of my work. There are other paths to this function besides powerpc. I feel that the kernel should keep running instead of halting. Regards, -- Michael W. Bringmann Linux Technology Center IBM Corporation Tie-Line 363-5196 External: (512) 286-5196 Cell: (512) 466-0650 mwb@linux.vnet.ibm.com