linux-kernel - Re: [PULL] x86 cpumask work

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Message-ID: <20090316084802.GB1062@elte.hu>
Date:	Mon, 16 Mar 2009 09:48:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org, x86@...nel.org,
	Mike Travis <travis@....com>
Subject: Re: [PULL] x86 cpumask work


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Sunday 15 March 2009 16:30:44 Ingo Molnar wrote:
> > 
> > >  	} else if (check_c1e_idle(c)) {
> > >  		printk(KERN_INFO "using C1E aware idle routine\n");
> > > -		alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
> > > -		cpumask_clear(c1e_mask);
> > > +		/* c1e_mask can only be NULL during boot of first cpu. */
> > > +		if (c1e_mask == NULL) {
> > > +			alloc_cpumask_var(&c1e_mask, GFP_KERNEL);
> > 
> > Sigh, there are two bugs here:
> > 
> >    1) what if the GFP_KERNEL allocation fails?
> 
> As the comments says, it can only be NULL during boot of the first CPU.
> 
> start_kernel -> check_bugs -> identify_boot_cpu -> identify_cpu
>   -> select_idle_routine.
> 
> Did you want me to panic if it fails?

Ah, ok. But i think it's very unobvious to embedd a "once per 
bootup" dynamic allocation like that. Please put it into a 
separate init routine instead. That way select_idle() [which 
runs during every CPU hotplug event] wont have this allocation.

	Ingo
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