2013/5/20 Borislav Petkov <b...@alien8.de>: > On Mon, May 20, 2013 at 11:16:33AM +0800, Michael Wang wrote: >> I suppose the reason is that the cpu we passed to >> mod_delayed_work_on() has a chance to become offline before we >> disabled irq, what about check it before send resched ipi? like: > > I think this is only addressing the symptoms - what we should be doing > instead is asking ourselves why are we even scheduling work on a cpu if > the machine goes offline? > > I don't know though who should be responsible for killing all that > work - the workqueue itself or the guy who created it, i.e. cpufreq > governor... > > Hmmm.
Let's look at this portion of cpu_down(): err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu)); if (err) { /* CPU didn't die: tell everyone. Can't complain. */ smpboot_unpark_threads(cpu); cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu); goto out_release; } BUG_ON(cpu_online(cpu)); /* * The migration_call() CPU_DYING callback will have removed all * runnable tasks from the cpu, there's only the idle task left now * that the migration thread is done doing the stop_machine thing. * * Wait for the stop thread to go away. */ while (!idle_cpu(cpu)) cpu_relax(); /* This actually kills the CPU. */ __cpu_die(cpu); /* CPU is completely dead: tell everyone. Too late to complain. */ cpu_notify_nofail(CPU_DEAD | mod, hcpu); check_for_tasks(cpu); The CPU is considered offline after the take_cpu_down stop machine job completes. But the struct timer_list timers are migrated later through CPU_DEAD notification. Only once that's completed we check for illegal residual tasks in the CPU. So there is a little window between the stop machine thing and __cpu_die() where a timer can fire with cpu_online(cpu) == 1. Now concerning the workqueue I don't know. I guess the per cpu ones are not migrated due to their affinity. Apparently they can still wake up and execute works due to the timers... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/