linux-kernel - Re: [RFC][PATCH 1/2] x86, fpu: wrap get_xsave

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Date:	Fri, 30 Jan 2015 19:28:05 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave@...1.net>
Cc:	dave.hansen@...ux.intel.com, riel@...hat.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, fenghua.yu@...el.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 1/2] x86, fpu: wrap get_xsave_addr() to make it
	safer

On 01/30, Dave Hansen wrote:
>
> +void *tsk_get_xsave_field(struct task_struct *tsk, int xsave_field)
> +{
> +	union thread_xstate *xstate;
> +
> +	unlazy_fpu(tsk);

ack, but to remind this depends on 2/3 I sent.

> +	xstate = tsk->thread.fpu.state;
> +	/*
> +	 * This might be unallocated if the FPU
> +	 * was never in use.
> +	 */
> +	if (!xstate)
> +		return NULL;

This is cosmetic, unlazy_fpu() is safe if !xstate, __thread_has_fpu()
is not possible in this case.

But perhaps

	if (!used_math())
		return NULL;

will look better.

Oleg.

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