[S390] switch_to: dont restore/save access & fpu regs for kernel threads

[deliverable/linux.git] / arch / s390 / include / asm / system.h

diff --git a/arch/s390/include/asm/system.h b/arch/s390/include/asm/system.h
index 1f2ebc4afd828f47da56d6763be4a16ba713263c..c35d0a383f0015759efb8ecf6f2eedfba343c385 100644 (file)
--- a/arch/s390/include/asm/system.h
+++ b/arch/s390/include/asm/system.h
@@ -85,14 +85,18 @@ static inline void restore_access_regs(unsigned int *acrs)
        asm volatile("lam 0,15,%0" : : "Q" (*acrs));
 }
 
-#define switch_to(prev,next,last) do {                                      \
-       if (prev == next)                                                    \
-               break;                                                       \
-       save_fp_regs(&prev->thread.fp_regs);                                 \
-       restore_fp_regs(&next->thread.fp_regs);                              \
-       save_access_regs(&prev->thread.acrs[0]);                             \
-       restore_access_regs(&next->thread.acrs[0]);                          \
-       prev = __switch_to(prev,next);                                       \
+#define switch_to(prev,next,last) do {                                 \
+       if (prev == next)                                               \
+               break;                                                  \
+       if (prev->mm) {                                                 \
+               save_fp_regs(&prev->thread.fp_regs);                    \
+               save_access_regs(&prev->thread.acrs[0]);                \
+       }                                                               \
+       if (next->mm) {                                                 \
+               restore_fp_regs(&next->thread.fp_regs);                 \
+               restore_access_regs(&next->thread.acrs[0]);             \
+       }                                                               \
+       prev = __switch_to(prev,next);                                  \
 } while (0)
 
 extern void account_vtime(struct task_struct *, struct task_struct *);