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Date: Tue, 27 Sep 2011 19:32:19 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Stephen Wilson <wilsons@start.ca>, linux-kernel@vger.kernel.org
Subject: Re: Q: x86: add context tag to mark mm when running a task in 32-bit
 compatibility mode
Message-ID: <20110927183219.GL2203@ZenIV.linux.org.uk>
References: <20110927170448.GA15977@redhat.com>
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On Tue, Sep 27, 2011 at 07:04:48PM +0200, Oleg Nesterov wrote:
> --- x/arch/x86/kernel/process_64.c
> +++ x/arch/x86/kernel/process_64.c
> @@ -502,10 +502,6 @@ void set_personality_64bit(void)
>  	/* Make sure to be in 64bit mode */
>  	clear_thread_flag(TIF_IA32);
>  
> -	/* Ensure the corresponding mm is not marked. */
> -	if (current->mm)
> -		current->mm->context.ia32_compat = 0;

What happens when 32bit task does exec on 64bit binary?

> -	if (current->mm)
> -		current->mm->context.ia32_compat = 1;
> +	set_bit(MMF_COMPAT, &current->mm->flags);

... assuming current->mm is never NULL here.