__compute_return_epc() uses CFC1 instruction which might result in a

coprocessor unusable exception since the process can lose its fpu
context by preemption.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

2 files changed, 14 insertions, 5 deletions

diff --git a/arch/mips/kernel/branch.c b/arch/mips/kernel/branch.c
index 01117e977a7f..56aea5f526a7 100644
--- a/arch/mips/kernel/branch.c
+++ b/arch/mips/kernel/branch.c
@@ -12,6 +12,7 @@
 #include <asm/branch.h>
 #include <asm/cpu.h>
 #include <asm/cpu-features.h>
+#include <asm/fpu.h>
 #include <asm/inst.h>
 #include <asm/ptrace.h>
 #include <asm/uaccess.h>
@@ -161,10 +162,13 @@ int __compute_return_epc(struct pt_regs *regs)
          * And now the FPA/cp1 branch instructions.
          */
         case cop1_op:
-                if (!cpu_has_fpu)
-                        fcr31 = current->thread.fpu.soft.fcr31;
-                else
+                preempt_disable();
+                if (is_fpu_owner())
                         asm volatile("cfc1\t%0,$31" : "=r" (fcr31));
+                else
+                        fcr31 = current->thread.fpu.hard.fcr31;
+                preempt_enable();
+
                 bit = (insn.i_format.rt >> 2);
                 bit += (bit != 0);
                 bit += 23;
diff --git a/include/asm-mips/fpu.h b/include/asm-mips/fpu.h
index ea24e733b1bc..9c828b1f8218 100644
--- a/include/asm-mips/fpu.h
+++ b/include/asm-mips/fpu.h
@@ -80,9 +80,14 @@ do {									\
 
 #define clear_fpu_owner()       clear_thread_flag(TIF_USEDFPU)
 
+static inline int __is_fpu_owner(void)
+{
+        return test_thread_flag(TIF_USEDFPU);
+}
+
 static inline int is_fpu_owner(void)
 {
-        return cpu_has_fpu && test_thread_flag(TIF_USEDFPU);
+        return cpu_has_fpu && __is_fpu_owner();
 }
 
 static inline void own_fpu(void)
@@ -127,7 +132,7 @@ static inline void restore_fp(struct task_struct *tsk)
 static inline fpureg_t *get_fpu_regs(struct task_struct *tsk)
 {
         if (cpu_has_fpu) {
-                if ((tsk == current) && is_fpu_owner())
+                if ((tsk == current) && __is_fpu_owner())
                         _save_fp(current);
                 return tsk->thread.fpu.hard.fpr;
         }