linux-kernel - Re: Oops with strace

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Message-ID: <alpine.LFD.1.10.0805081700570.3318@apollo.tec.linutronix.de>
Date:	Thu, 8 May 2008 17:02:08 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
cc:	Eric Sesterhenn <snakebyte@....de>, Ingo Molnar <mingo@...e.hu>,
	Frederik Deweerdt <deweerdt@...e.fr>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: Oops with strace_test

On Wed, 7 May 2008, Suresh Siddha wrote:
> On Wed, May 07, 2008 at 07:26:20PM +0200, Thomas Gleixner wrote:
> > 
> > Ok, we decoded the problem in meantime. Suresh will send a patch soon.
> 
> Appended patch should fix it. Eric, can you please check if it fixes the issue?
> I have to fix the math-emu aswell. But I will send a different patch for it.

Suresh,

looks good. Applied to x86.git. Waiting for Erics confirmation.

Thanks,
	tglx
 
> thanks,
> suresh
> ---
> 
> [patch] fix fpu restore during sig return
> 
> If the task never used fpu, initialize the fpu before restoring the FP state
> from the signal handler context. This will allocate the fpu state,
> if the task never needed it before.
> 
> Signed-off-by: Suresh Siddha <suresh.b.siddha@...el.com>
> ---
> 
> diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
> index db6839b..45e19ee 100644
> --- a/arch/x86/kernel/i387.c
> +++ b/arch/x86/kernel/i387.c
> @@ -450,7 +450,6 @@ static inline int restore_i387_fsave(struct _fpstate_ia32 __user *buf)
>  {
>  	struct task_struct *tsk = current;
>  
> -	clear_fpu(tsk);
>  	return __copy_from_user(&tsk->thread.xstate->fsave, buf,
>  				sizeof(struct i387_fsave_struct));
>  }
> @@ -461,7 +460,6 @@ static int restore_i387_fxsave(struct _fpstate_ia32 __user *buf)
>  	struct user_i387_ia32_struct env;
>  	int err;
>  
> -	clear_fpu(tsk);
>  	err = __copy_from_user(&tsk->thread.xstate->fxsave, &buf->_fxsr_env[0],
>  			       sizeof(struct i387_fxsave_struct));
>  	/* mxcsr reserved bits must be masked to zero for security reasons */
> @@ -478,6 +476,16 @@ int restore_i387_ia32(struct _fpstate_ia32 __user *buf)
>  	int err;
>  
>  	if (HAVE_HWFP) {
> +		struct task_struct *tsk = current;
> +		
> +		clear_fpu(tsk);
> +
> +		if (!used_math()) {
> +			err = init_fpu(tsk);
> +			if (err)
> +				return err;
> +		}
> +		
>  		if (cpu_has_fxsr)
>  			err = restore_i387_fxsave(buf);
>  		else
> diff --git a/include/asm-x86/i387.h b/include/asm-x86/i387.h
> index da2adb4..6b722d3 100644
> --- a/include/asm-x86/i387.h
> +++ b/include/asm-x86/i387.h
> @@ -175,7 +175,15 @@ static inline int save_i387(struct _fpstate __user *buf)
>   */
>  static inline int restore_i387(struct _fpstate __user *buf)
>  {
> -	set_used_math();
> +	struct task_struct *tsk = current;
> +	int err;
> +
> +	if (!used_math()) {
> +		err = init_fpu(tsk);
> +		if (err)
> +			return err;
> +	}
> +
>  	if (!(task_thread_info(current)->status & TS_USEDFPU)) {
>  		clts();
>  		task_thread_info(current)->status |= TS_USEDFPU;
> 
--
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