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Tue, 28 Oct 2025 04:44:06 GMT Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D8FF920043; Tue, 28 Oct 2025 04:44:05 +0000 (GMT) Received: from smtpav07.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D632520040; Tue, 28 Oct 2025 04:44:02 +0000 (GMT) Received: from [9.109.204.116] (unknown [9.109.204.116]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 28 Oct 2025 04:44:02 +0000 (GMT) Message-ID: Date: Tue, 28 Oct 2025 10:14:01 +0530 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] powerpc/kexec: Enable SMT before waking offline CPUs To: "Nysal Jan K.A." , Madhavan Srinivasan , Christophe Leroy Cc: Sachin P Bappalige , stable@vger.kernel.org, Michael Ellerman , Nicholas Piggin , Laurent Dufour , Thomas Gleixner , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <20251025080512.85690-1-nysal@linux.ibm.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: <20251025080512.85690-1-nysal@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=JqL8bc4C c=1 sm=1 tr=0 ts=69004a1b cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=QyXUC8HyAAAA:8 a=VnNF1IyMAAAA:8 a=FNYM6xYWznnmATNcaFQA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-GUID: FxmdnNuzaqm78WhLlnDMk9_nePRBgCOm X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDI1MDAxOSBTYWx0ZWRfX7QkWKQhFuOOO V9MA81mTt9sfU1UD8Rq3/20G1aeAxSbe8CFEPB7VnCN4pwya45IxorLcSrfBcX/F6suOnwW34CB Cn8L+SYmX9LxK5UTibbSis7CZckp43117R0xE1ZoGvcKAR26z2hgFrCxVqzDNkUDPwdVjnydw6F qJtIDFi5uh0mstIzJE2S80w7QpJ/nSfhGhz56vsYUOXVqyCGhYsfa+fhCe0+PUUj5Laj+HfKzak r7JBMdSnqeEcAuWlskJqzOpcPoS4z5X46mGRWD1vQVnPbWUJdjYwUiPaZU0UAV6tMyWZ/ScVEJF MYK+a9KsRBkULhLeZdBs7iit8B0uR6Ct4rQ7+JvafBgR5EkDr3KH9OPlUMa+qld4QCne36e25ZQ YvNeualAVKZNQLfjbKa7yFGgbnSQoA== X-Proofpoint-ORIG-GUID: lthnj5OCypztazoUVbkfPZXSBi221ky3 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-28_02,2025-10-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 clxscore=1011 lowpriorityscore=0 malwarescore=0 bulkscore=0 priorityscore=1501 spamscore=0 adultscore=0 phishscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510020000 definitions=main-2510250019 Hello Nysal, On 25/10/25 13:35, Nysal Jan K.A. wrote: > If SMT is disabled or a partial SMT state is enabled, when a new kernel > image is loaded for kexec, on reboot the following warning is observed: > > kexec: Waking offline cpu 228. > WARNING: CPU: 0 PID: 9062 at arch/powerpc/kexec/core_64.c:223 kexec_prepare_cpus+0x1b0/0x1bc > [snip] > NIP kexec_prepare_cpus+0x1b0/0x1bc > LR kexec_prepare_cpus+0x1a0/0x1bc > Call Trace: > kexec_prepare_cpus+0x1a0/0x1bc (unreliable) > default_machine_kexec+0x160/0x19c > machine_kexec+0x80/0x88 > kernel_kexec+0xd0/0x118 > __do_sys_reboot+0x210/0x2c4 > system_call_exception+0x124/0x320 > system_call_vectored_common+0x15c/0x2ec > > This occurs as add_cpu() fails due to cpu_bootable() returning false for > CPUs that fail the cpu_smt_thread_allowed() check or non primary > threads if SMT is disabled. > > Fix the issue by enabling SMT and resetting the number of SMT threads to > the number of threads per core, before attempting to wake up all present > CPUs. > > Fixes: 38253464bc82 ("cpu/SMT: Create topology_smt_thread_allowed()") > Reported-by: Sachin P Bappalige > Cc: stable@vger.kernel.org # v6.6+ > Signed-off-by: Nysal Jan K.A. > --- > arch/powerpc/kexec/core_64.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c > index 222aa326dace..ff6df43720c4 100644 > --- a/arch/powerpc/kexec/core_64.c > +++ b/arch/powerpc/kexec/core_64.c > @@ -216,6 +216,11 @@ static void wake_offline_cpus(void) > { > int cpu = 0; > > + lock_device_hotplug(); > + cpu_smt_num_threads = threads_per_core; > + cpu_smt_control = CPU_SMT_ENABLED; Above variables are  #define if CONFIG_SMP and CONFIG_HOTPLUG_SMT is not there. I think the above code should go under #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT). Seems like the build failure reported below is also pointing the same issue: https://lore.kernel.org/all/202510280824.Fe2D1Sbw-lkp@intel.com/ > + unlock_device_hotplug(); > + > for_each_present_cpu(cpu) { > if (!cpu_online(cpu)) { > printk(KERN_INFO "kexec: Waking offline cpu %d.\n",