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From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH repost] sched: export sched_set/getaffinity to modules
Date: Sun, 4 Jul 2010 12:00:05 +0300
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Cc: Peter Zijlstra <peterz@infradead.org>,
	Sridhar Samudrala <sri@us.ibm.com>, Tejun Heo <tj@kernel.org>,
	Ingo Molnar <mingo@elte.hu>, netdev <netdev@vger.kernel.org>,
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	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Dmitri Vorobiev <dmitri.vorobiev@movial.com>,
	Jiri Kosina <jkosina@suse.cz>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andi Kleen <ak@linux.intel.com>
To: Oleg Nesterov <oleg@redhat.com>
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On Fri, Jul 02, 2010 at 11:06:37PM +0200, Oleg Nesterov wrote:
> On 07/02, Peter Zijlstra wrote:
> >
> > On Fri, 2010-07-02 at 11:01 -0700, Sridhar Samudrala wrote:
> > >
> > >  Does  it (Tejun's kthread_clone() patch) also  inherit the
> > > cgroup of the caller?
> >
> > Of course, its a simple do_fork() which inherits everything just as you
> > would expect from a similar sys_clone()/sys_fork() call.
> 
> Yes. And I'm afraid it can inherit more than we want. IIUC, this is called
> from ioctl(), right?
> 
> Then the new thread becomes the natural child of the caller, and it shares
> ->mm with the parent. And files, dup_fd() without CLONE_FS.
> 
> Signals. Say, if you send SIGKILL to this new thread, it can't sleep in
> TASK_INTERRUPTIBLE or KILLABLE after that. And this SIGKILL can be sent
> just because the parent gets SIGQUIT or abother coredumpable signal.
> Or the new thread can recieve SIGSTOP via ^Z.
> 
> Perhaps this is OK, I do not know. Just to remind that kernel_thread()
> is merely clone(CLONE_VM).
> 
> Oleg.


Right. Doing this might break things like flush.  The signal and exit
behaviour needs to be examined carefully. I am also unsure whether
using such threads might be more expensive than inheriting kthreadd.

-- 
MST