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Date: Wed, 26 Oct 2016 20:31:34 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Oleg Nesterov <oleg@redhat.com>
cc: Andy Lutomirski <luto@amacapital.net>,
        Roman Pen <roman.penyaev@profitbricks.com>,
        Andy Lutomirski <luto@kernel.org>,
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        Tejun Heo <tj@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/1] kthread: allocate kthread structure using
 kmalloc
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References: <20161025110508.9052-1-roman.penyaev@profitbricks.com> <20161025140333.GB4326@redhat.com> <20161025154301.GA12015@redhat.com> <CALCETrVmczve=knhYGrcXkeAXRQR_oY4ac2BSc7V0TEnx6-GFA@mail.gmail.com> <20161026141359.GA6893@redhat.com>
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On Wed, 26 Oct 2016, Oleg Nesterov wrote:
> On 10/26, Thomas Gleixner wrote:
> >
> > On Wed, 26 Oct 2016, Oleg Nesterov wrote:
> > > +static inline void set_kthread_struct(void *kthread)
> > > +{
> > > +	/*
> > > +	 * We abuse ->set_child_tid to avoid the new member and because it
> > > +	 * can't be wrongly copied by copy_process(). We also rely on fact
> > > +	 * that the caller can't exec, so PF_KTHREAD can't be cleared.
> > > +	 */
> > > +	current->set_child_tid = (__force void __user *)kthread;
> >
> > Can we pretty please avoid this type casting? We only have 5 places using
> > set_child_tid. So we can really make it a proper union
> 
> Yes, I thought about anonymous union too, the only problem is that
> it will need more comments ;)

Be careful with anonymous unions. There are a few pitfalls with older
compilers. That's why I said make it a proper union and fixup the 5 usage
sites. It might work in this case, but you've been warned :)

Thanks,

	tglx