Re: [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread()

Borislav Petkov
2015-03-13T10:54:22Z

On Wed, Mar 11, 2015 at 06:35:07PM +0100, Oleg Nesterov wrote:
> drop_init_fpu() makes no sense. We need drop_fpu() and only if

Oh, please explain why. I can try to rhyme it up as something like "we
don't need to restore FPU context when flushing the thread" but I'm not
sure...

> !use_eager_fpu().
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> arch/x86/kernel/process.c | 11 ++++-------
> 1 files changed, 4 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index c396de2..2e71120 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -131,14 +131,11 @@ void flush_thread(void)
> flush_ptrace_hw_breakpoint(tsk);
> memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
>
> - drop_init_fpu(tsk);
> - /*
> - * Free the FPU state for non xsave platforms. They get reallocated
> - * lazily at the first use.
> - */
> - if (!use_eager_fpu())
> + if (!use_eager_fpu()) {
> + /* FPU state will be reallocated lazily at the first use. */
> + drop_fpu(tsk);
> free_thread_xstate(tsk);
> - else if (!used_math()) {
> + } else if (!used_math()) {
> /* kthread execs. TODO: cleanup this horror. */
> if (WARN_ON(init_fpu(current)))
> force_sig(SIGKILL, current);

Also, can we clean up the tsk/current usage here?

We assign current to tsk and we work with it but then later use current
again. Needlessly confusing.

Thanks.

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
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