Messages in this thread | | | Subject | Re: [PATCH] sched/kthread: Complain loudly when others violate our flags | From | Steven Rostedt <> | Date | Fri, 30 Sep 2011 00:05:29 -0400 |
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On Thu, 2011-09-29 at 20:48 -0700, Tejun Heo wrote: > > > WTF is the workqueue code setting the PF_THREAD_BOUND flag manually? > > Talk about fragile coupling! You just made this flag meaningless. Don't > > do that. > > IIRC, this was because there was no way to set PF_THREAD_BOUND once a > kthread starts to run and workers can stay active across CPU bring > down/up cycle. Per-cpu kthreads need PF_THREAD_BOUND to prevent cpu > affinity manipulation by third party for correctness.
That third party also includes workqueue. It shouldn't mess with that flag.
> > > Sorry but I just wasted two whole days because of this nonsense and I'm > > not particularly happy about it. > > Sorry that it wasted your time and made you unhappy but wouldn't > grepping for its usage a logical thing if you wanted to add to what it > meant? PF_THREAD_BOUND meaning the task's affinity or cpuset can't be > manipulated by third party seems like a valid interpretation.
But you set PF_THREAD_BOUND to tasks that ARE NOT BOUNDED! That's just wrong. It's not about "don't touch this affinity" it's about, this thread has been pinned to a CPU and will not change for the life of the thread.
> > Simply removing it would allow breaking workqueue from userland by > manipulating affinity. How about testing PF_WQ_WORKER in > set_cpus_allowed_ptr() (and maybe cpuset, I'm not sure)?
Do you realize that these threads migrate? If you didn't, it just proves that you shouldn't touch it.
-- Steve
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