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Tue, 14 Jul 2026 13:08:50 +0000 (GMT) Received: from [9.124.218.91] (unknown [9.124.218.91]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 14 Jul 2026 13:08:49 +0000 (GMT) Message-ID: <39fc9f4b-b93e-4c53-b1d4-4c868c18ac62@linux.ibm.com> Date: Tue, 14 Jul 2026 18:38:49 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 11/12] virt/steal_monitor: Act on steal time periodically and decide on preferred CPUs To: Yury Norov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org References: <20260709215648.1246821-1-sshegde@linux.ibm.com> <20260709215648.1246821-12-sshegde@linux.ibm.com> <9da4fd45-0a0f-495d-8207-816ee88c5937@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzE0MDEzMiBTYWx0ZWRfX/JmcsyqC6q+r VPaiDsp1AqaDo6UYDTw8Sylfzzzeh1rpRqXT1+Ofdx+tOI5UWCXm38YiAM338UXUu41uwkkDDFr CJCHinv9RBEKFhV9sCy3g2c6MPBqFF0= X-Authority-Analysis: v=2.4 cv=Mp1iLWae c=1 sm=1 tr=0 ts=6a5634ee cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=3PJ_pY2KotYQqXn6dpYA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: Bf-fc0mQ7Qc0C-W4QUItlV-xXxnF28dK X-Proofpoint-ORIG-GUID: _dbRl5ysoEfH4FezUuHubov7NIv64A0K X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzE0MDEzMiBTYWx0ZWRfXz3j65nZhYlFZ 7O5iYnRycDqN0WstymVfhT/ZCglOYgW0h05iuNKWLyZ0uLjACzKZ9aZIFS5VamxXazwwY2q+UV6 P3Fdod2LXRKLHXtX2vI991pifLaoF3SKvhJ4QeNXJCjt7NXgVTX0GMcpV1grT2LIlObSpUNsEcP W+y77U1V12Gc31DAx/iVHtgrTXmYy/PVEFQqvbxyCRS+hdvbxZFyGuuqhfQNQi8LZysuTdDL/Dh UoaAmMoxZCjSDe0B4aqbCXCsZ4AAD4IVDo8amIFu3nGxNMxx47C/gvHx7FWgEGle/pFWBm2B6wS K2xW1Ot6jJwbKdxszmr6SS+vyKiQs6jY5jRbRAXciKGFiTrprjjB9xVS5uB+eQo0bS9Du4MDB8e oz9FkJHSymY1zJksksLWKU+EnYZ9IaefxZVoxwxu1NEmEjG96cewK00eSLWCYZpWNPoYIF78Ogo rmuW5ag+YSJEpO8bGJQ== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-14_03,2026-07-10_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 bulkscore=0 spamscore=0 malwarescore=0 lowpriorityscore=0 impostorscore=0 priorityscore=1501 suspectscore=0 clxscore=1015 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607140132 Hi Yury. On 7/14/26 6:01 PM, Yury Norov wrote: > On Mon, Jul 13, 2026 at 11:18:59AM +0530, Shrikanth Hegde wrote: > > ... > >>>> +requeue_work: >>>> + /* maintain design constructs always */ >>>> + WARN_ON_ONCE(cpumask_empty(cpu_preferred_mask)); >>>> + WARN_ON_ONCE(!cpumask_subset(cpu_preferred_mask, cpu_active_mask)); >>> >>> cpu_read_lock here? And again, you should do something to restore >>> integrity. WARN_ON is not enough. The simplest and safest thing you >>> can do is to unload the driver. You definitely shouldn't schedule a >>> new work against the broken cpu_preferred_mask. >> >> How about not requeue the work if it broken. Add a pr_err and return. >> That makes driver pretty much nop until rmmod. >> >> /* maintain design constructs always */ >> if (cpumask_empty(cpu_preferred_mask)) { >> pr_err("empty cpu_preferred_mask, stop steal_monitor work"); >> return; >> } >> >> if (!cpumask_subset(cpu_preferred_mask, cpu_active_mask)) { >> pr_err("preferred: %*pbl is not a subset of active: %*pbl, stop steal_monitor work\n", >> pr_cpuamsk_args(cpu_preferred_mask), pr_cpuamsk_args(cpu_active_mask)); >> return; >> } > > That would keep broken preferred cpumask working in the kernel. > > Imagine, it becomes empty on Friday night. That severely hurts > the scheduling on the VMs. So, your approach requires the VM > admin to come and manually rmmod the driver. This is not how > he wanted to spend the evening, I guess. :) > > So, ether unload the driver, or actively recover the invariant. yes, i will restore it to the active mask and not requeue the work and add a pr_err. > Can we unload the driver after init completes? This is happening in work function after module is loaded. This invariant maybe broken after a few days driver was loaded. > Thanks, > Yury