On Mon, 2013-05-27 at 11:57 +0530, 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
this check, r8 no longer contains the expected TI_FLAGS information.

Hrm, the code was supposed to still have TI_FLAGS in r8 and mostly does
until the 

	andis.	r8,r8,_TIF_EMULATE_STACK_STORE@h

Was added which clobbers it.

Can't we just fix the above to use a different destination register ?
r0 looks fair game at this point...
 

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.

Ben.