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Date: Fri, 6 Mar 2015 15:17:50 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@kernel.org>, David Vrabel <david.vrabel@citrix.com>
Cc: Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bp@suse.de>,
        Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Pekka Riikonen <priikone@iki.fi>, Rik van Riel <riel@redhat.com>,
        Suresh Siddha <sbsiddha@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        "Yu, Fenghua" <fenghua.yu@intel.com>,
        Quentin Casasnovas <quentin.casasnovas@oracle.com>
Subject: Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly
	disable irqs
Message-ID: <20150306141750.GA23787@redhat.com>
References: <54F74F59.5070107@intel.com> <20150305195127.GA12657@redhat.com> <20150305195149.GB12657@redhat.com> <20150305201101.GA21571@gmail.com> <20150305212532.GA16890@redhat.com> <20150306075833.GA623@gmail.com> <20150306132634.GA20693@redhat.com> <20150306134601.GA11718@gmail.com> <20150306140154.GA22811@redhat.com>
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On 03/06, Oleg Nesterov wrote:
>
> On 03/06, Ingo Molnar wrote:
> >
> > How about the patch from David Vrabel? That seems to solve the
> > irq-disable problem too, right?
>
> I wasn't cc'ed, I guess you mean
>
> 	[PATCHv4] x86, fpu: remove the logic of non-eager fpu mem allocation at the first usage
> 	http://marc.info/?l=linux-kernel&m=142564237705311&w=2
>
> Not sure I understand it correctly after the first quick look, but
>
> 1. It conflicts with the recent changes in tip/x86/fpu
>
> 2. fpu_ini() initializes current->thread.fpu.state. This looks unneeded,
>    the kernel threads no longer have FPU context and do not abuse CPU.
>
> 3. I can be easily wrong, but it looks buggy... Note that
>    arch_dup_task_struct() doesn't allocate child->fpu.state if
>    !tsk_used_math(parent).
>
> Add David...
>
> No, I do not think this patch is a good idea. Perhaps I am wrong, but I
> think we need other changes. And they should start from init_fpu().

But the change in eager_fpu_init_bp() looks good (on top of tip/x86/fpu),
at least I was going to do the same ;)

In any case, I do not think this patch can target -stable.

Oleg.