powerpc/32bit:Store temporary result in r0 instead of r8

Commit a9c4e541ea9b22944da356f2a9258b4eddcc953b
"powerpc/kprobe: Complete kprobe and migrate exception frame"
introduced a regression:

While returning from exception handling in case of PREEMPT enabled,
_TIF_NEED_RESCHED bit is checked in TI_FLAGS (thread_info flag) of current
task. Only if this bit is set, it should continue with the process of
calling preempt_schedule_irq() to schedule highest priority task if
available.

Current code assumes that r8 contains TI_FLAGS and check this for
_TIF_NEED_RESCHED, but as r8 is modified in the code which executes before
this check, r8 no longer contains the expected TI_FLAGS information.

As a result check for comparison with _TIF_NEED_RESCHED was failing even if
NEED_RESCHED bit is set in the current thread_info flag. Due to this,
preempt_schedule_irq() and in turn scheduler was not getting called even if
highest priority task is ready for execution.

So, store temporary results in r0 instead of r8 to prevent r8 from getting
modified as subsequent code is dependent on its value.

Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
CC: <stable@vger.kernel.org> [v3.7+]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index d22e73e4618b7924879517f1f59cb99dcd63b43e..22b45a4955cd8f03a26c89a7fb2ab79252f2b6d4 100644 (file)
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -849,7 +849,7 @@ resume_kernel:
        /* check current_thread_info, _TIF_EMULATE_STACK_STORE */
        CURRENT_THREAD_INFO(r9, r1)
        lwz     r8,TI_FLAGS(r9)
-       andis.  r8,r8,_TIF_EMULATE_STACK_STORE@h
+       andis.  r0,r8,_TIF_EMULATE_STACK_STORE@h
        beq+    1f
 
        addi    r8,r1,INT_FRAME_SIZE    /* Get the kprobed function entry */