On Fri, Feb 06, 2015 at 03:02:00PM -0500, r...@redhat.com wrote:
> From: Oleg Nesterov <o...@redhat.com>
>
> math_error() calls save_init_fpu() after conditional_sti(), this means
> that the caller can be preempted. If !use_eager_fpu() we can hit the
> WARN_ON_ONCE(!__thread_has_fpu(tsk)) and/or save the wrong FPU state.
>
> Change math_error() to use unlazy_fpu() and kill save_init_fpu().
>
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
> Signed-off-by: Rik van Riel <r...@redhat.com>
> ---
> arch/x86/include/asm/fpu-internal.h | 18 ------------------
> arch/x86/kernel/traps.c | 2 +-
> 2 files changed, 1 insertion(+), 19 deletions(-)
>
> diff --git a/arch/x86/include/asm/fpu-internal.h
> b/arch/x86/include/asm/fpu-internal.h
> index 0dbc08282291..27d00e04f911 100644
> --- a/arch/x86/include/asm/fpu-internal.h
> +++ b/arch/x86/include/asm/fpu-internal.h
> @@ -520,24 +520,6 @@ static inline void __save_fpu(struct task_struct *tsk)
> }
>
> /*
> - * These disable preemption on their own and are safe
> - */
> -static inline void save_init_fpu(struct task_struct *tsk)
> -{
> - WARN_ON_ONCE(!__thread_has_fpu(tsk));
> -
> - if (use_eager_fpu()) {
> - __save_fpu(tsk);
> - return;
> - }
> -
> - preempt_disable();
> - __save_init_fpu(tsk);
> - __thread_fpu_end(tsk);
> - preempt_enable();
> -}
> -
> -/*
> * i387 state interaction
> */
> static inline unsigned short get_fpu_cwd(struct task_struct *tsk)
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index fb4cb6adf225..51c465846f06 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -663,7 +663,7 @@ static void math_error(struct pt_regs *regs, int
> error_code, int trapnr)
> /*
> * Save the info for the exception handler and clear the error.
> */
> - save_init_fpu(task);
> + unlazy_fpu(task);
Do I see it correctly that even with this there's a not-so-small hole
*after* conditional_sti() and *before* unlazy_fpu() where caller can
still get preempted?
Thanks.
--
Regards/Gruss,
Boris.
ECO tip #101: Trim your mails when you reply.
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