Thanks!
On 04/27, Bobby Powers wrote:
>
> v2: switch used_math() -> tsk_used_math(tsk) to consistently use the
> grabbed tsk instead of current, like in the rest of flush_thread().
>
> Oleg's commit f893959b ("x86/fpu: Don't abuse drop_init_fpu() in
> flush_thread()") removed drop_init_fpu() usage from flush_thread.
> This seems to break things for me - the Go 1.4 test suite fails all
> over the place with floating point comparision errors (offending
> commit found through bisection).
>
> The functional change was that flush_thread after f893959b only calls
> restore_init_xstate when both use_eager_fpu() and !used_math() are
> true. drop_init_fpu (now fpu_reset_state) calls restore_init_xstate()
> regardless of whether current used_math() - apply the same logic here.
>
> Fixes: f893959b ("x86/fpu: Don't abuse drop_init_fpu() in flush_thread()")
> Signed-off-by: Bobby Powers <[email protected]>
> Acked-by: Oleg Nesterov <[email protected]>
> Cc: Andi Kleen <[email protected]>
> Cc: Borislav Petkov <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Andy Lutomirski <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Fenghua Yu <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Cc: Pekka Riikonen <[email protected]>
> Cc: Quentin Casasnovas <[email protected]>
> Cc: Rik van Riel <[email protected]>
> Cc: Suresh Siddha <[email protected]>
> ---
> arch/x86/kernel/process.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 8213da6..1a6fcf8 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -156,11 +156,13 @@ void flush_thread(void)
> /* FPU state will be reallocated lazily at the first use. */
> drop_fpu(tsk);
> free_thread_xstate(tsk);
> - } else if (!used_math()) {
> - /* kthread execs. TODO: cleanup this horror. */
> - if (WARN_ON(init_fpu(tsk)))
> - force_sig(SIGKILL, tsk);
> - user_fpu_begin();
> + } else {
> + if (!tsk_used_math(tsk)) {
> + /* kthread execs. TODO: cleanup this horror. */
> + if (WARN_ON(init_fpu(tsk)))
> + force_sig(SIGKILL, tsk);
> + user_fpu_begin();
> + }
> restore_init_xstate();
> }
> }
> --
> 2.3.6
>
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