[PATCH 27/33] x86/fpu: Simplify fpu__activate_fpstate_read()

[Ingo Molnar]

fpu__activate_fpstate_read() can only ever be called for a non-current,
non-executing (stopped) task - so make sure this is checked via a warning
and remove the current-task logic.

This also fixes an incorrect (but harmless) warning introduced by one of
the earlier patches.

Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Eric Biggers <ebigge...@gmail.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
 arch/x86/kernel/fpu/core.c | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 93103a909c47..7bd4edb76c1d 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -256,26 +256,18 @@ EXPORT_SYMBOL_GPL(fpu__activate_curr);
  *
  * If the task has not used the FPU before then initialize its
  * fpstate.
- *
- * If the task has used the FPU before then save it.
  */
 void fpu__activate_fpstate_read(struct fpu *fpu)
 {
-       /*
-        * If fpregs are active (in the current CPU), then
-        * copy them to the fpstate:
-        */
-       if (fpu->fpstate_active) {
-               fpu__save(fpu);
-       } else {
-               if (!fpu->fpstate_active) {
-                       fpstate_init(&fpu->state);
-                       trace_x86_fpu_init_state(fpu);
+       WARN_ON_FPU(fpu == &current->thread.fpu);
 
-                       trace_x86_fpu_activate_state(fpu);
-                       /* Safe to do for current and for stopped child tasks: 
*/
-                       fpu->fpstate_active = 1;
-               }
+       if (!fpu->fpstate_active) {
+               fpstate_init(&fpu->state);
+               trace_x86_fpu_init_state(fpu);
+
+               trace_x86_fpu_activate_state(fpu);
+               /* Safe to do for current and for stopped child tasks: */
+               fpu->fpstate_active = 1;
        }
 }
 
-- 
2.11.0