linux-kernel - Re: [PATCH 01/16] x86, fpu: wrap get_xsave

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Message-ID: <20150422155840.GJ6897@pd.tnic>
Date:	Wed, 22 Apr 2015 17:58:40 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	Dave Hansen <dave@...1.net>, linux-kernel@...r.kernel.org,
	x86@...nel.org, dave.hansen@...ux.intel.com, riel@...hat.com,
	sbsiddha@...il.com, luto@...capital.net, mingo@...hat.com,
	hpa@...or.com, fenghua.yu@...el.com
Subject: Re: [PATCH 01/16] x86, fpu: wrap get_xsave_addr() to make it safer

On Wed, Apr 22, 2015 at 05:32:45PM +0200, Oleg Nesterov wrote:
> How? I am certainly missing you point... OK, please forge about FPU.
> Consider this code:
> 
> 	tsk = current;
> 	for (;;)
> 		BUG_ON(tsk != current);
> 
> it doesn't need to disable preemption. We do not care if CPU switches
> to another thread, even if this thread executes the same code. Because
> its tsk/current will differ, but "tsk == current" will be still true.
> 
> Could you please spell?

Bah, forget what I said. tglx schooled me on IRC. We always do get
called with tsk == current. Sorry for the confusion...

> See above... used_math() should be correct because we know that tsk==current,
> but I agree that tsk_used_math(tsk) looks better.

Right, and it is clear what's going on, even to lusers like me.

Thanks for teaching me guys.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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