MIPS: Fix race condition with FPU thread task flag during context switch.

[ralf@linux-mips.org: Cosmetic changes; also fixed up r2300_switch.S and
octeon_switch.S which needed similar modifications.]

Signed-off-by: Leonid Yegoshin <yegoshin@mips.com>
Signed-off-by: Steven J. Hill <sjhill@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3784/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

4 files changed, 11 insertions, 24 deletions

diff --git a/arch/mips/include/asm/switch_to.h b/arch/mips/include/asm/switch_to.h
index 5d33621b565..4f8ddba8c36 100644
--- a/arch/mips/include/asm/switch_to.h
+++ b/arch/mips/include/asm/switch_to.h
@@ -22,7 +22,7 @@ struct task_struct;
  * switch_to(n) should switch tasks to task nr n, first
  * checking that n isn't the current task, in which case it does nothing.
  */
-extern asmlinkage void *resume(void *last, void *next, void *next_ti);
+extern asmlinkage void *resume(void *last, void *next, void *next_ti, u32 __usedfpu);
 
 extern unsigned int ll_bit;
 extern struct task_struct *ll_task;
@@ -66,11 +66,13 @@ do {									\
 
 #define switch_to(prev, next, last)                                     \
 do {                                                                    \
+        u32 __usedfpu;                                                  \
         __mips_mt_fpaff_switch_to(prev);                                \
         if (cpu_has_dsp)                                                \
                 __save_dsp(prev);                                       \
         __clear_software_ll_bit();                                      \
-        (last) = resume(prev, next, task_thread_info(next));            \
+        __usedfpu = test_and_clear_tsk_thread_flag(prev, TIF_USEDFPU);  \
+        (last) = resume(prev, next, task_thread_info(next), __usedfpu); \
 } while (0)
 
 #define finish_arch_switch(prev)                                        \
diff --git a/arch/mips/kernel/octeon_switch.S b/arch/mips/kernel/octeon_switch.S
index ce89c806170..0441f54b2a6 100644
--- a/arch/mips/kernel/octeon_switch.S
+++ b/arch/mips/kernel/octeon_switch.S
@@ -31,7 +31,7 @@
 
 /*
  * task_struct *resume(task_struct *prev, task_struct *next,
- *                     struct thread_info *next_ti)
+ *                     struct thread_info *next_ti, int usedfpu)
  */
         .align  7
         LEAF(resume)
diff --git a/arch/mips/kernel/r2300_switch.S b/arch/mips/kernel/r2300_switch.S
index 293898391e6..9c51be5a163 100644
--- a/arch/mips/kernel/r2300_switch.S
+++ b/arch/mips/kernel/r2300_switch.S
@@ -43,7 +43,7 @@
 
 /*
  * task_struct *resume(task_struct *prev, task_struct *next,
- *                     struct thread_info *next_ti) )
+ *                     struct thread_info *next_ti, int usedfpu)
  */
 LEAF(resume)
         mfc0    t1, CP0_STATUS
@@ -51,18 +51,9 @@ LEAF(resume)
         cpu_save_nonscratch a0
         sw      ra, THREAD_REG31(a0)
 
-        /*
-         * check if we need to save FPU registers
-         */
-        lw      t3, TASK_THREAD_INFO(a0)
-        lw      t0, TI_FLAGS(t3)
-        li      t1, _TIF_USEDFPU
-        and     t2, t0, t1
-        beqz    t2, 1f
-        nor     t1, zero, t1
+        beqz    a3, 1f
 
-        and     t0, t0, t1
-        sw      t0, TI_FLAGS(t3)
+        PTR_L   t3, TASK_THREAD_INFO(a0)
 
         /*
          * clear saved user stack CU1 bit
diff --git a/arch/mips/kernel/r4k_switch.S b/arch/mips/kernel/r4k_switch.S
index 9414f935446..42d2a393842 100644
--- a/arch/mips/kernel/r4k_switch.S
+++ b/arch/mips/kernel/r4k_switch.S
@@ -41,7 +41,7 @@
 
 /*
  * task_struct *resume(task_struct *prev, task_struct *next,
- *                     struct thread_info *next_ti)
+ *                     struct thread_info *next_ti, int usedfpu)
  */
         .align  5
         LEAF(resume)
@@ -53,16 +53,10 @@
         /*
          * check if we need to save FPU registers
          */
-        PTR_L   t3, TASK_THREAD_INFO(a0)
-        LONG_L  t0, TI_FLAGS(t3)
-        li      t1, _TIF_USEDFPU
-        and     t2, t0, t1
-        beqz    t2, 1f
-        nor     t1, zero, t1
 
-        and     t0, t0, t1
-        LONG_S  t0, TI_FLAGS(t3)
+        beqz    a3, 1f
 
+        PTR_L   t3, TASK_THREAD_INFO(a0)
         /*
          * clear saved user stack CU1 bit
          */