Messages in this thread | | | Date | Tue, 13 Jan 2015 17:50:43 +0100 | From | Oleg Nesterov <> | 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, Rik van Riel 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?
Yes, see xfpregs_get/set. So I think this change is not needed (but I didn't look at the next patches).
Oleg.
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