x86/fpu: Add debugging check to fpu__save()

Document the function a bit more and add debugging check that we are only
running this with the current task.

Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index ac47278..66f1053 100644 (file)
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -119,9 +119,13 @@ EXPORT_SYMBOL(__kernel_fpu_end);
 
 /*
  * Save the FPU state (initialize it if necessary):
+ *
+ * This only ever gets called for the current task.
  */
 void fpu__save(struct task_struct *tsk)
 {
+       WARN_ON(tsk != current);
+
        preempt_disable();
        if (__thread_has_fpu(tsk)) {
                if (use_eager_fpu()) {