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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 19 Feb 2019 20:03:13 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x1JK3CQ519005648 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 19 Feb 2019 20:03:12 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9458AB2068; Tue, 19 Feb 2019 20:03:12 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3A6FFB2065; Tue, 19 Feb 2019 20:03:11 +0000 (GMT) Received: from oc6857751186.ibm.com (unknown [9.80.225.63]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 19 Feb 2019 20:03:11 +0000 (GMT) Subject: Re: [PATCH] powerpc/pseries: Fix dn reference error in dlpar_cpu_remove_by_index To: Michael Bringmann , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Nicholas Piggin , Rob Herring , "Juliet M. Kim" , Nathan Lynch , Thomas Falcon References: From: Tyrel Datwyler Date: Tue, 19 Feb 2019 12:03:10 -0800 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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19021920-2213-0000-0000-000003546BFC X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010627; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000281; SDB=6.01163442; UDB=6.00607479; IPR=6.00944025; MB=3.00025659; MTD=3.00000008; XFM=3.00000015; UTC=2019-02-19 20:03:15 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19021920-2214-0000-0000-00005D68C804 Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-02-19_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=8.0.1-1810050000 definitions=main-1902190140 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/19/2019 07:46 AM, Michael Bringmann wrote: > powerpc/pseries: Fix dn reference error in dlpar_cpu_remove_by_index() > > A reference to the device node of the CPU to be removed is released > upon successful removal of the associated CPU device. If the call > to remove the CPU device fails, dlpar_cpu_remove_by_index() still > frees the reference and this leads to miscomparisons and/or > addressing errors later on. > > This problem may be observed when trying to DLPAR 'hot-remove' a CPU > from a system that has only a single CPU. The operation will fail > because there is no other CPU to which the kernel operations may be > migrated, but the refcount will still be decremented. > > Signed-off-by: Michael Bringmann > > > diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c > index 97feb6e..9537bb9 100644 > --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c > +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c > @@ -635,7 +635,8 @@ static int dlpar_cpu_remove_by_index(u32 drc_index) > } > > rc = dlpar_cpu_remove(dn, drc_index); > - of_node_put(dn); > + if (!rc) > + of_node_put(dn); > return rc; > } > NACK! The logic here is wrong. Here is the full function. static int dlpar_cpu_remove_by_index(u32 drc_index) { struct device_node *dn; int rc; dn = cpu_drc_index_to_dn(drc_index); if (!dn) { pr_warn("Cannot find CPU (drc index %x) to remove\n", drc_index); return -ENODEV; } rc = dlpar_cpu_remove(dn, drc_index); of_node_put(dn); return rc; } The call to cpu_drc_index_to_dn() returns a device_node with the reference count incremented. So, regardless of the success or failure of the call to dlpar_cpu_remove() you need to release that reference. If there is a reference counting issue it is somewhere else. -Tyrel