From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754726AbbCMKyW (ORCPT <rfc822;w@1wt.eu>);
	Fri, 13 Mar 2015 06:54:22 -0400
Received: from cantor2.suse.de ([195.135.220.15]:41662 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751547AbbCMKyT (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 13 Mar 2015 06:54:19 -0400
Date: Fri, 13 Mar 2015 11:52:51 +0100
From: Borislav Petkov <bp@suse.de>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Hansen <dave.hansen@intel.com>, Ingo Molnar <mingo@kernel.org>,
        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 4/4] x86/fpu: don't abuse drop_init_fpu() in
 flush_thread()
Message-ID: <20150313105251.GD31998@pd.tnic>
References: <54F74F59.5070107@intel.com>
 <20150311173346.GB5032@redhat.com>
 <20150311173507.GF5032@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20150311173507.GF5032@redhat.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Mar 11, 2015 at 06:35:07PM +0100, Oleg Nesterov wrote:
> drop_init_fpu() makes no sense. We need drop_fpu() and only if

Oh, please explain why. I can try to rhyme it up as something like "we
don't need to restore FPU context when flushing the thread" but I'm not
sure...

> !use_eager_fpu().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  arch/x86/kernel/process.c |   11 ++++-------
>  1 files changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index c396de2..2e71120 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -131,14 +131,11 @@ void flush_thread(void)
>  	flush_ptrace_hw_breakpoint(tsk);
>  	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
>  
> -	drop_init_fpu(tsk);
> -	/*
> -	 * Free the FPU state for non xsave platforms. They get reallocated
> -	 * lazily at the first use.
> -	 */
> -	if (!use_eager_fpu())
> +	if (!use_eager_fpu()) {
> +		/* FPU state will be reallocated lazily at the first use. */
> +		drop_fpu(tsk);
>  		free_thread_xstate(tsk);
> -	else if (!used_math()) {
> +	} else if (!used_math()) {
>  		/* kthread execs. TODO: cleanup this horror. */
>  		if (WARN_ON(init_fpu(current)))
>  			force_sig(SIGKILL, current);

Also, can we clean up the tsk/current usage here?

We assign current to tsk and we work with it but then later use current
again. Needlessly confusing.

Thanks.

-- 
Regards/Gruss,
    Boris.

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