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

Oleg Nesterov
2015-01-13T16:20:38Z

On 01/11, riel@redhat.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 ?

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

Oleg.