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Sat, 22 Feb 2020 00:00:30 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by userp3020.oracle.com with ESMTP id 2y8ud7vec6-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 22 Feb 2020 00:00:30 +0000 Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 01M00SuG007204; Sat, 22 Feb 2020 00:00:29 GMT Received: from ca-dmjordan1.us.oracle.com (/10.211.9.48) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 21 Feb 2020 16:00:28 -0800 Date: Fri, 21 Feb 2020 19:00:45 -0500 From: Daniel Jordan To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Daniel Jordan , Eric Biggers , Herbert Xu , Steffen Klassert , linux-crypto@vger.kernel.org, Sasha Levin Subject: Re: [PATCH 4.19 061/191] padata: always acquire cpu_hotplug_lock before pinst->lock Message-ID: <20200222000045.cl45vclfhvkjursm@ca-dmjordan1.us.oracle.com> References: <20200221072250.732482588@linuxfoundation.org> <20200221072258.745173144@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200221072258.745173144@linuxfoundation.org> User-Agent: NeoMutt/20180716 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9538 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 bulkscore=0 malwarescore=0 mlxlogscore=503 suspectscore=0 adultscore=0 spamscore=0 mlxscore=0 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002210180 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9538 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 lowpriorityscore=0 suspectscore=0 spamscore=0 priorityscore=1501 adultscore=0 mlxscore=0 clxscore=1011 malwarescore=0 mlxlogscore=552 phishscore=0 impostorscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002210180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 21, 2020 at 08:40:34AM +0100, Greg Kroah-Hartman wrote: > From: Daniel Jordan > > [ Upstream commit 38228e8848cd7dd86ccb90406af32de0cad24be3 ] > > lockdep complains when padata's paths to update cpumasks via CPU hotplug > and sysfs are both taken: > > # echo 0 > /sys/devices/system/cpu/cpu1/online > # echo ff > /sys/kernel/pcrypt/pencrypt/parallel_cpumask > > ====================================================== > WARNING: possible circular locking dependency detected > 5.4.0-rc8-padata-cpuhp-v3+ #1 Not tainted > ------------------------------------------------------ > bash/205 is trying to acquire lock: > ffffffff8286bcd0 (cpu_hotplug_lock.rw_sem){++++}, at: padata_set_cpumask+0x2b/0x120 > > but task is already holding lock: > ffff8880001abfa0 (&pinst->lock){+.+.}, at: padata_set_cpumask+0x26/0x120 > > which lock already depends on the new lock. I think this patch should be dropped from all stable queues (4.4, 4.9, 4.14, 4.19, 5.4, and 5.5). The main benefit is to un-break lockdep for testing with future padata changes, and an actual deadlock seems unlikely. These stable versions don't fix the ordering in padata_remove_cpu() either (nothing calls it though). I tried the other stable padata patch in this cycle ("padata: validate cpumask without removed CPU during offline"), it passed my tests and should stay in. thanks, Daniel