Messages in this thread | | | Date | Tue, 21 Apr 2009 21:37:24 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH v3 1/1] ftrace, workqueuetrace: Make workqueuetracepoints use TRACE_EVENT macro |
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On 04/21, Frederic Weisbecker wrote: > > On Tue, Apr 21, 2009 at 05:28:43PM +0200, Oleg Nesterov wrote: > > More precisely, at this stage tsk->cpu_allowed is not bound, it has > > "all CPUS", == cpu_possible_mask. This means that cpumask_first() > > returns the "random" value. The fix is simple, I think you should > > just add "int cpu" argument to cleanup_workqueue_thread(). > > Ok. > But where is it done? I mean, by looking at workqueue_cpu_callback() > in workqueue.c, I only see this part related to _cpu_down(): > > case CPU_POST_DEAD: > cleanup_workqueue_thread(cwq); > break;
There are two case. Please note that create_workqueue_thread() does not bind the thread, we delay kthread_bind() untill start_workqueue_thread(). So, if we have CPU_UP_CANCELED (after CPU_UP_PREPARE) we call cleanup_workqueue_thread() but the thread still has ->cpu_allowed == cpu_all_mask.
Another case is a normal cpu_down(). When CPU_POST_DEAD happens, this CPU is really dead. All tasks were alredy moved from the dead cpu. And since wq_thread was affine to that CPU, it gets the "full" cpu mask.
OK, I don't think it is possible to parse the text above ;) Please look at /* No more Mr. Nice Guy. */ in move_task_off_dead_cpu().
Oleg.
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