x86/fpu: Always restore_xinit_state() when use_eager_cpu()

The following commit:

  f893959b0898 ("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 this commit
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.

Switch used_math() -> tsk_used_math(tsk) to consistently use the grabbed
tsk instead of current, like in the rest of flush_thread().

Tested-by: Dave Hansen <[email protected]>
Signed-off-by: Bobby Powers <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: H. Peter Anvin <[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]>
Cc: Thomas Gleixner <[email protected]>
Fixes: f893959b ("x86/fpu: Don't abuse drop_init_fpu() in flush_thread()")
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index bfc99b3b6522078ba2aea707b24d6aa513e1bf7d..6e338e3b1dc04cc69ab41c012fe5671cc25321cd 100644 (file)
--- 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();
        }
 }