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d2518e49-3d5b-4a2f-ffd5-08dd235d0323 X-MS-Exchange-CrossTenant-AuthSource: PH0PR10MB4472.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Dec 2024 14:20:55.0110 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: r51X1hphmwXLw2rIASAVWe8phQWoUDdYn53FK3FxPt0C13MzrEFXTdnnIXKBS8lyAYGJPjYHwDMjIzrAY89taw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH0PR10MB4826 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1057,Hydra:6.0.680,FMLib:17.12.68.34 definitions=2024-12-23_06,2024-12-23_01,2024-11-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 suspectscore=0 malwarescore=0 mlxscore=0 spamscore=0 mlxlogscore=999 phishscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2411120000 definitions=main-2412230129 X-Proofpoint-ORIG-GUID: RhlzcZvSrhOdfJRu5L3QpO3Xcu_1W-NR X-Proofpoint-GUID: RhlzcZvSrhOdfJRu5L3QpO3Xcu_1W-NR Hello Hillf, On 23/12/2024 11:51 pm, Hillf Danton wrote: > On Mon, 23 Dec 2024 11:14:21 +1100 imran.f.khan@oracle.com >> >> Recently we have come across some bugs in the RDS code, where a delayed >> work was being queued on an offlined CPU and as a result of that the > > Such a queue could not happen given irq disabled in queue_delayed_work_on(). > Did you see it upstream? > You mean upstream RDS or upstream workqueue ? For RDS I need to check, but with upstream v6.6 kernel, I was able to submit a delayed work to an offlined CPU. The delayed work would never happen and I can see corresponding timer in timer list of offlined CPU (using crash). Once the CPU is brought back online, depending on the workload the work handler gets executed. I used following test module: =============== #include #include #include #include #include #include #include #include #define TIMEOUT 1 /* test timeout in secs */ #define NUM_WORK_ITEMS 1 /* number of work items to submit */ static DEFINE_MUTEX(mutex); static DEFINE_MUTEX(dwork_func_mutex); static void delayed_work_func(struct work_struct *data) { int cpu; mutex_lock(&dwork_func_mutex); cpu = get_cpu(); pr_err("%s invoked for work: 0x%px on cpu#%d \n", __func__, data, cpu); put_cpu(); mutex_unlock(&dwork_func_mutex); } static int param_set_queue_work_on_cpu(const char *val, const struct kernel_param *kp) { int cpu, this_cpu, i; struct delayed_work *dwork = NULL; if (!mutex_trylock(&mutex)) return -EBUSY; cpu = simple_strtoul(val, NULL, 0); /*if (!cpu_present(cpu)) return -EINVAL;*/ for (i = 0; i < NUM_WORK_ITEMS; i++) { dwork = kzalloc(sizeof(struct delayed_work), GFP_KERNEL); if(dwork) { this_cpu = get_cpu(); INIT_DELAYED_WORK(dwork, delayed_work_func); queue_delayed_work_on(cpu, system_wq, dwork, msecs_to_jiffies(10000)); pr_err("Submitted dwork 0x%px on %s cpu#%d \n", dwork, cpu_online(cpu)?"online":"offline", cpu); put_cpu(); } } mutex_unlock(&mutex); return 0; } module_param_call(queue_work_on_cpu, param_set_queue_work_on_cpu, NULL, NULL, 0600); static int __init workqueue_study_init(void) { pr_err("module_init \n"); return 0; } static void workqueue_study_exit(void) { pr_err("module_exit \n"); } MODULE_AUTHOR("Imran Khan "); MODULE_DESCRIPTION("Workqueue study"); MODULE_LICENSE("GPL"); module_init(workqueue_study_init); module_exit(workqueue_study_exit); =========== This module gives an interface at: /sys/module//params/queue_work_on_cpu Writing X there would submit a delayed_work (delay 10 secs) to CPU X. We can see if CPU X is online, submitted work gets executed after around 10 secs. But if CPU X is offline, the submitted work handler does not get fired unless the CPU has been brought back online. Thanks, Imran >> underlying timer was not firing, which in turn meant that the work was >> never able to make it to the intended worker_pool.