From: Steven Rostedt <rostedt@goodmis.org>
To: Tejun Heo <htejun@gmail.com>
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: Fri, 30 Sep 2011 00:05:29 -0400 [thread overview]
Message-ID: <1317355529.4588.45.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <20110930034815.GF10425@mtj.dyndns.org>
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
next prev parent reply other threads:[~2011-09-30 4:05 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
2011-09-30 4:05 ` Steven Rostedt [this message]
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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