linux-kernel - Re: [PATCH v3 1/1] kthread: allocate kthread structure using kmalloc

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Message-ID: <alpine.DEB.2.20.1610262027110.5013@nanos>
Date:   Wed, 26 Oct 2016 20:31:34 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Oleg Nesterov <oleg@...hat.com>
cc:     Andy Lutomirski <luto@...capital.net>,
        Roman Pen <roman.penyaev@...fitbricks.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] kthread: allocate kthread structure using
 kmalloc

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