From: Tejun Heo <htejun@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] sched/kthread: Complain loudly when others violate our flags
Date: Thu, 29 Sep 2011 20:48:15 -0700 [thread overview]
Message-ID: <20110930034815.GF10425@mtj.dyndns.org> (raw)
In-Reply-To: <1317158254.26514.55.camel@gandalf.stny.rr.com>
Hello, Steven.
Sorry about the delay, coming back from a rather long vacation.
On Tue, Sep 27, 2011 at 05:17:34PM -0400, Steven Rostedt wrote:
> I looked at the task that it tried to migrate, and it happened to be the
> kworker thread! Then I went into kernel/workqueue.c and found this
> nonsense:
>
> if (bind && !on_unbound_cpu)
> kthread_bind(worker->task, gcwq->cpu);
> else {
> worker->task->flags |= PF_THREAD_BOUND;
> if (on_unbound_cpu)
> worker->flags |= WORKER_UNBOUND;
> }
>
> Nothing but the scheduler and kthread_bind() has the right to set the
> PF_THREAD_BOUND flag. Especially when the thread IS NOT BOUNDED!!!!!!
>
> I don't go around and stick my hand down your pants to play with your
> flags! Don't stick your hand in ours and play with our flags!
>
> 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.
> 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.
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)?
Thanks.
--
tejun
next prev parent reply other threads:[~2011-09-30 3:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-27 21:17 Steven Rostedt
2011-09-28 0:22 ` Thomas Gleixner
2011-09-30 3:48 ` Tejun Heo [this message]
2011-09-30 4:05 ` Steven Rostedt
2011-09-30 4:14 ` Tejun Heo
2011-09-30 8:34 ` Peter Zijlstra
2011-09-30 8:55 ` Tejun Heo
2011-09-30 9:04 ` Peter Zijlstra
2011-10-03 1:15 ` Tejun Heo
2011-10-03 10:20 ` Peter Zijlstra
2011-10-07 1:40 ` Tejun Heo
2011-10-03 10:33 ` Peter Zijlstra
2011-10-03 13:43 ` Thomas Gleixner
2011-10-03 10:50 ` Peter Zijlstra
2011-09-30 9:23 ` Peter Zijlstra
2011-09-30 9:29 ` Peter Zijlstra
2011-09-30 9:27 ` Peter Zijlstra
2011-10-03 1:22 ` Tejun Heo
2011-09-30 3:55 ` Tejun Heo
2011-09-30 4:08 ` Steven Rostedt
2011-09-30 4:28 ` Tejun Heo
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