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Thu, 25 Jun 2026 16:47:03 +0000 (GMT) Received: from pfw153.pfw.tadn.ibm.com (unknown [9.5.7.52]) by smtpav05.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 25 Jun 2026 16:47:03 +0000 (GMT) From: Ninad Palsule To: eajames@linux.ibm.com, linux@roeck-us.net, psanman@juniper.net, arnd@arndb.de, ninad@linux.ibm.com, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v1 1/1] hwmon: (occ) Fix sysfs device unreg deadlock Date: Thu, 25 Jun 2026 11:46:53 -0500 Message-ID: <20260625164700.2797362-2-ninad@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260625164700.2797362-1-ninad@linux.ibm.com> References: <20260625164700.2797362-1-ninad@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-hwmon@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=X4Ni7mTe c=1 sm=1 tr=0 ts=6a3d5b8a cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=PO-QMXBumzaoU13EfK0A:9 X-Proofpoint-Spam-Info: AW1haW4tMjYwNjI1MDE0MCBTYWx0ZWRfX2gYzI6fNfRXp kBh0MtQADi7a8CQrs9b+8aaxtW3GV/xGDYFnCNN8A8SeyJvhG0k3rlNa6/5e7VsLXz9ef53HQbg 9RdTMual6MOOxUCBivvorI/1FWWcy7Y= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjI1MDE0MCBTYWx0ZWRfX/93yR2PoLStd awyzEjzjo7NO5TPAxK5DmSk8patP/dTap3BCgqE5WeK9xUmKYTUrWvTS1y9qGUQZCPNyqZ9W5Xo IDzV/XiNhueJHhJEhVBgN4gCWCb5v+Le2w6o9RtEb25zM7gTV8BTB6Gqcl5xl0hgwll0Mi/qSXw 9MUxQx7nCoVejj94AMimWI32FCusl/P9Tpw48HC/5EBewtyF1UjLxEO1ZJRjrt9HQ6/ZAAFFxY0 PgqCHjMo8BR9Z5sjy6wwEr0qeTWg/r0Sv6qsuUjyX1Zl+P0zAvKt6u0YItzlNcUaAb2Wkrx1BCp MGJsLaVKPjZlf/pgce8qO8IqQFp+s2w6Wa7uRdODgzu/tAvr7WUJCCLKIabzsAIxFI1IiyAQZbw zxEPycISw/J/QGwdN/r0Sq0xAiJuFTcmIXOf4IV7YN8bcjz6eDcuXPza8h4nYPvd7MJdd1NDGyU MJz6nw5axEjGN8hmQjg== X-Proofpoint-ORIG-GUID: xh16AkkNjfoKkHqqDM5qVU6o33PG2rJ9 X-Proofpoint-GUID: xh16AkkNjfoKkHqqDM5qVU6o33PG2rJ9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-25_02,2026-06-24_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 bulkscore=0 suspectscore=0 spamscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606250140 Release the driver lock before unregistering the hwmon device to prevent a deadlock. The device_unregister() call can block waiting for sysfs operations to complete, but those operations may be blocked waiting for the same lock held during unregistration. The deadlock occurs when: 1. Thread A holds the driver lock and calls device_unregister() 2. device_unregister() waits for sysfs operations to drain 3. Thread B is blocked in a sysfs read operation waiting for the driver lock 4. Neither thread can proceed, causing a hung task This was observed during power system remote restart operations when concurrent sysfs accesses occurred during OCC active state transitions. Kernel log excerpt showing the deadlock: INFO: task openpower-occ-c:1430 blocked for more than 122 seconds. Call trace: schedule+0x28/0xfc kernfs_drain+0xc8/0x174 __kernfs_remove.part.0+0x138/0x21c kernfs_remove_by_name_ns+0x7c/0xcc [...] device_unregister+0x1c/0x5c hwmon_device_unregister+0x58/0xb0 occ_active+0x6c/0xe74 occ_active_store+0x54/0x80 Reproducer: Run these two scripts in parallel: Script 1 (continuous sysfs read): while true; do cat /sys/class/hwmon/hwmon14/power15_cap_user done Script 2 (OCC active state toggle): while true; do echo 0 > /sys/bus/platform/drivers/occ-hwmon/occ-hwmon.1/occ_active echo 1 > /sys/bus/platform/drivers/occ-hwmon/occ-hwmon.1/occ_active sleep 0.2 done Signed-off-by: Ninad Palsule --- drivers/hwmon/occ/common.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/hwmon/occ/common.c b/drivers/hwmon/occ/common.c index 42cc6068bb08..a5641dbbba2f 100644 --- a/drivers/hwmon/occ/common.c +++ b/drivers/hwmon/occ/common.c @@ -1149,15 +1149,22 @@ int occ_active(struct occ *occ, bool active) goto unlock; } } else { + struct device *hwmon_dev = occ->hwmon; + if (!occ->active) { rc = -EALREADY; goto unlock; } - if (occ->hwmon) - hwmon_device_unregister(occ->hwmon); occ->active = false; occ->hwmon = NULL; + + mutex_unlock(&occ->lock); + + if (hwmon_dev) + hwmon_device_unregister(hwmon_dev); + + return 0; } unlock: -- 2.51.0