linux-kernel - Re: [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from memory if task is traced

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Message-ID: <54B548EA.7020005@redhat.com>
Date:	Tue, 13 Jan 2015 11:33:46 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	matt.fleming@...el.com, bp@...e.de, pbonzini@...hat.com,
	tglx@...utronix.de, luto@...capital.net
Subject: Re: [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from
 memory if task is traced

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On 01/13/2015 11:19 AM, Oleg Nesterov wrote:
> On 01/11, riel@...hat.com wrote:
>> 
>> @@ -412,8 +412,14 @@ static inline void switch_fpu_prepare(struct
>> task_struct *old, struct task_struc bool preload =
>> tsk_used_math(new) && (use_eager_fpu() || new->thread.fpu_counter
>> > 5); if (__thread_has_fpu(old)) { -		if (!__save_init_fpu(old)) 
>> +		/* +		 * Make sure the FPU state is restored from memory next
>> time, +		 * if the task has an FPU exception pending, or the
>> task's in +		 * memory FPU state could be changed by a debugger. 
>> +		 */ +		if (!__save_init_fpu(old) ||
>> task_is_stopped_or_traced(old)) cpu = ~0;
> 
> Well, if debugger wants to change FPU state, it should call
> init_fpu() which resets .last_cpu ?

Does the ptrace (and utrace, and ... ) code actually do that?

> Plus "is_stopped" is not needed, ptracer no longer can do STOPPED
> -> TRACED transition.

I will remove _is_stopped.

- -- 
All rights reversed
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