Hi Tejun Two years ago, I reported a bug in workqueues - a work item that is supposed to be bound to a specific CPU can be migrated to a different CPU when the origianl CPU is disabled by writing zero to /sys/devices/system/cpu/cpu*/online This causes crashes in dm-crypt, because it assumes that a work item stays on the same CPU. There was some discussion (see here http://www.redhat.com/archives/dm-devel/2012-March/msg00034.html ), but the bug is still unfixed and I've just got another bug report about dm-crypt crashing because of it. I'd like to ask - are you going to fix the workqueue code so that work item migrations can't happen? - or are you going to specify that work item migration can happen and do you require that all code that relies on the fact that a work item executes on a single CPU be fixed? Here I'm sending a simple kernel module that shows the bug. Mikulas /* * A proof of concept that a work item executed on a workqueue may change CPU * when CPU hot-unplugging is used. * Compile this as a module and run: * insmod test.ko; sleep 1; echo 0 >/sys/devices/system/cpu/cpu1/online * You see that the work item starts executing on CPU 1 and ends up executing * on different CPU, usually 0. */ #include <linux/module.h> #include <linux/delay.h> static struct workqueue_struct *wq; static struct work_struct work; static void do_work(struct work_struct *w) { printk("starting work on cpu %d\n", smp_processor_id()); msleep(10000); printk("finishing work on cpu %d\n", smp_processor_id()); } static int __init test_init(void) { printk("module init\n"); wq = alloc_workqueue("testd", WQ_MEM_RECLAIM | WQ_CPU_INTENSIVE, 1); if (!wq) { printk("alloc_workqueue failed\n"); return -ENOMEM; } INIT_WORK(&work, do_work); queue_work_on(1, wq, &work); return 0; } static void __exit test_exit(void) { destroy_workqueue(wq); printk("module exit\n"); } module_init(test_init) module_exit(test_exit) MODULE_LICENSE("GPL"); -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
