On 05/27/2013 02:27 PM, Priyanka Jain wrote:
Add instruction to load TI_FLAGS in r8
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
Could you elaborate this scenario? As I take a look at this path:
...
/* Clear _TIF_EMULATE_STACK_STORE flag */
lis r11,_TIF_EMULATE_STACK_STORE@h
addi r5,r9,TI_FLAGS
0: lwarx r8,0,r5
andc r8,r8,r11
#ifdef CONFIG_IBM405_ERR77
dcbt 0,r5
#endif
stwcx. r8,0,r5
bne- 0b
1:
#ifdef CONFIG_PREEMPT
/* check current_thread_info->preempt_count */
lwz r0,TI_PREEMPT(r9)
cmpwi 0,r0,0 /* if non-zero, just restore regs and return */
bne restore
andi. r8,r8,_TIF_NEED_RESCHED
...
Where is R8 clobbered?
Tiejun
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.
Signed-off-by: Priyanka Jain <priyanka.j...@freescale.com>
---
arch/powerpc/kernel/entry_32.S | 1 +
1 files changed, 1 insertions(+), 0 deletions(-)
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index d22e73e..0239c7f 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -887,6 +887,7 @@ resume_kernel:
#ifdef CONFIG_PREEMPT
/* check current_thread_info->preempt_count */
lwz r0,TI_PREEMPT(r9)
+ lwz r8,TI_FLAGS(r9)
cmpwi 0,r0,0 /* if non-zero, just restore regs and return */
bne restore
andi. r8,r8,_TIF_NEED_RESCHED
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